MySQL經常使用函數介紹

　　　　　　　　　　　　　　　　MySQL經常使用函數介紹　　　　　

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　做者：尹正傑

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一.操做符介紹

1>.操做符優先級　　

mysql> SELECT 10+20*30; +----------+
| 10+20*30 |
+----------+
|      610 |
+----------+
1 row in set (0.00 sec) mysql> mysql> SELECT (10+20)*30; +------------+
| (10+20)*30 |
+------------+
|        900 |
+------------+
1 row in set (0.00 sec) mysql> mysql>

若是想改變優先級執行順序，則可使用括號(mysql> SELECT (10+20)*30;)

2>.對比操做符

• 對比操做符的執行結果爲true,false,null三種 
• Between A and B 表明檢查值是否在A和B之間 
• Coalesce()表明返回第一個非Null的值 
• =表明相等操做符 
• >表明大於操做符 
• >=表明大於等於操做符 
• Greatest()表明返回最大的值 
• In()表明檢查值是否在一系列的值之中 
• Interval()表明返回比第一個參數小的參數的位置 
• is/is not表明檢查值是否與布爾值相同/不一樣 • Is not null表明檢查值是不是非NULL 
• Is null表明檢查值是不是NULL 
• Isnull()表明檢查參數是NULL 
• Least()表明返回最小的參數 • <表明小於操做符 
• <=表明小於等於操做符 
• Like表明字符匹配 
• Not between A and B表明檢查值是否不在A和B的範圍以內 • !=/<>表明不等於操做符 
• Not in()表明檢查值是否不在一系列值的當中 • Not like表明檢查值是否不匹配 
• Strcmp()對比兩個字符串

mysql> SELECT 1 = 0; +-------+
| 1 = 0 |
+-------+
|     0 |
+-------+
1 row in set (0.01 sec) mysql> mysql> SELECT "0" = 0; +---------+
| "0" = 0 |
+---------+
|       1 |
+---------+
1 row in set (0.00 sec) mysql> mysql> SELECT "0.0" = 0; +-----------+
| "0.0" = 0 |
+-----------+
|         1 |
+-----------+
1 row in set (0.00 sec) mysql> mysql> SELECT "0.0001" = 0; +--------------+
| "0.0001" = 0 |
+--------------+
|            0 |
+--------------+
1 row in set (0.00 sec) mysql> mysql> SELECT ".01" = 0.01; +--------------+
| ".01" = 0.01 |
+--------------+
|            1 |
+--------------+
1 row in set (0.01 sec) mysql>

「=」 對比操做符案例展現  

mysql> SELECT ".01" <> "0.01"; +-----------------+
| ".01" <> "0.01" |
+-----------------+
|               1 |
+-----------------+
1 row in set (0.00 sec) mysql> mysql> SELECT .01 <> "0.01"; +---------------+
| .01 <> "0.01" |
+---------------+
|             0 |
+---------------+
1 row in set (0.00 sec) mysql> mysql> SELECT .01 != "0.01"; +---------------+
| .01 != "0.01" |
+---------------+
|             0 |
+---------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT "yinzhengjie" <> "zhengjie"; +-----------------------------+
| "yinzhengjie" <> "zhengjie" |
+-----------------------------+
|                           1 |
+-----------------------------+
1 row in set (0.00 sec) mysql> SELECT "yinzhengjie" != "zhengjie"; +-----------------------------+
| "yinzhengjie" != "zhengjie" |
+-----------------------------+
|                           1 |
+-----------------------------+
1 row in set (0.00 sec) mysql>

"<>/!=" 對比操做符案例展現

mysql> SELECT 2 <= 3; +--------+
| 2 <= 3 |
+--------+
|      1 |
+--------+
1 row in set (0.00 sec) mysql> mysql> SELECT 3 <= 2; +--------+
| 3 <= 2 |
+--------+
|      0 |
+--------+
1 row in set (0.00 sec) mysql> mysql>

"<=" 小於等於對比操做符案例展現 

mysql> SELECT 100 < 200; +-----------+
| 100 < 200 |
+-----------+
|         1 |
+-----------+
1 row in set (0.00 sec) mysql> mysql> SELECT 100 < 100; +-----------+
| 100 < 100 |
+-----------+
|         0 |
+-----------+
1 row in set (0.00 sec) mysql> mysql>

"<" 小於對比操做符案例展現

mysql> SELECT 100 >= 200; +------------+
| 100 >= 200 |
+------------+
|          0 |
+------------+
1 row in set (0.00 sec) mysql> mysql> SELECT 200 >= 100; +------------+
| 200 >= 100 |
+------------+
|          1 |
+------------+
1 row in set (0.00 sec) mysql> mysql>

">=" 大於等於對比操做符

mysql> SELECT 200 > 100; +-----------+
| 200 > 100 |
+-----------+
|         1 |
+-----------+
1 row in set (0.00 sec) mysql> mysql> SELECT 100 > 200; +-----------+
| 100 > 200 |
+-----------+
|         0 |
+-----------+
1 row in set (0.00 sec) mysql>

">" 大於對比操做符

mysql> SELECT 100 IS TRUE, 0 IS FALSE, NULL IS UNKNOWN; +-------------+------------+-----------------+
| 100 IS TRUE | 0 IS FALSE | NULL IS UNKNOWN |
+-------------+------------+-----------------+
|           1 |          1 |               1 |
+-------------+------------+-----------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT 200 IS TRUE, 200 IS FALSE, 200 IS UNKNOWN; +-------------+--------------+----------------+
| 200 IS TRUE | 200 IS FALSE | 200 IS UNKNOWN |
+-------------+--------------+----------------+
|           1 |            0 |              0 |
+-------------+--------------+----------------+
1 row in set (0.00 sec) mysql> mysql> SELECT 0 IS TRUE, 0 IS FALSE, 0 IS UNKNOWN; +-----------+------------+--------------+
| 0 IS TRUE | 0 IS FALSE | 0 IS UNKNOWN |
+-----------+------------+--------------+
|         0 |          1 |            0 |
+-----------+------------+--------------+
1 row in set (0.00 sec) mysql> mysql> SELECT NULL IS TRUE, NULL IS FALSE, NULL IS UNKNOWN; +--------------+---------------+-----------------+
| NULL IS TRUE | NULL IS FALSE | NULL IS UNKNOWN |
+--------------+---------------+-----------------+
|            0 |             0 |               1 |
+--------------+---------------+-----------------+
1 row in set (0.00 sec) mysql>

"is" 操做符

mysql> SELECT 10 IS NOT UNKNOWN, 0 IS NOT UNKNOWN, NULL IS NOT UNKNOWN; +-------------------+------------------+---------------------+
| 10 IS NOT UNKNOWN | 0 IS NOT UNKNOWN | NULL IS NOT UNKNOWN |
+-------------------+------------------+---------------------+
|                 1 |                1 |                   0 |
+-------------------+------------------+---------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT 10 IS NOT TRUE,0 IS NOT FALSE,NULL IS NOT UNKNOWN; +----------------+----------------+---------------------+
| 10 IS NOT TRUE | 0 IS NOT FALSE | NULL IS NOT UNKNOWN |
+----------------+----------------+---------------------+
|              0 |              0 |                   0 |
+----------------+----------------+---------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT 10 IS NOT FALSE,0 IS NOT TRUE,NULL IS NOT UNKNOWN; +-----------------+---------------+---------------------+
| 10 IS NOT FALSE | 0 IS NOT TRUE | NULL IS NOT UNKNOWN |
+-----------------+---------------+---------------------+
|               1 |             1 |                   0 |
+-----------------+---------------+---------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT 10 IS NOT FALSE,0 IS NOT TRUE,100 IS NOT UNKNOWN; +-----------------+---------------+--------------------+
| 10 IS NOT FALSE | 0 IS NOT TRUE | 100 IS NOT UNKNOWN |
+-----------------+---------------+--------------------+
|               1 |             1 |                  1 |
+-----------------+---------------+--------------------+
1 row in set (0.00 sec) mysql>

"Is not" 操做符

mysql> SELECT 1 IS NULL, 0 IS NULL, NULL IS NULL; +-----------+-----------+--------------+
| 1 IS NULL | 0 IS NULL | NULL IS NULL |
+-----------+-----------+--------------+
|         0 |         0 |            1 |
+-----------+-----------+--------------+
1 row in set (0.00 sec) mysql> mysql>

"Is null" 對比操做符

mysql> SELECT 1 IS NOT NULL, 0 IS NOT NULL, NULL IS NOT NULL; +---------------+---------------+------------------+
| 1 IS NOT NULL | 0 IS NOT NULL | NULL IS NOT NULL |
+---------------+---------------+------------------+
|             1 |             1 |                0 |
+---------------+---------------+------------------+
1 row in set (0.00 sec) mysql>

"Is not null" 對比操做符

mysql> SELECT 2 BETWEEN 1 AND 3, 2 BETWEEN 3 and 1; +-------------------+-------------------+
| 2 BETWEEN 1 AND 3 | 2 BETWEEN 3 and 1 |
+-------------------+-------------------+
|                 1 |                 0 |
+-------------------+-------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT 1 BETWEEN 2 AND 3; +-------------------+
| 1 BETWEEN 2 AND 3 |
+-------------------+
|                 0 |
+-------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT'b'BETWEEN'a'AND'c'; +---------------------+
| 'b'BETWEEN'a'AND'c' |
+---------------------+
|                   1 |
+---------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT 2 BETWEEN 2 AND '3'; +---------------------+
| 2 BETWEEN 2 AND '3' |
+---------------------+
|                   1 |
+---------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT 2 BETWEEN 2 AND 'x-3'; +-----------------------+
| 2 BETWEEN 2 AND 'x-3' |
+-----------------------+
|                     0 |
+-----------------------+
1 row in set, 1 warning (0.00 sec) mysql>

"Expr between min and max" 對比操做符,至關於 "min <= expr AND expr <= max","expr NOT BETWEEN min AND max" 對比操做符至關於NOT(expr BETWEEN min AND max)

mysql> mysql> SELECT COALESCE(NULL,200); +--------------------+
| COALESCE(NULL,200) |
+--------------------+
|                200 |
+--------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT COALESCE(NULL,NULL,NULL); +--------------------------+
| COALESCE(NULL,NULL,NULL) |
+--------------------------+
|                     NULL |
+--------------------------+
1 row in set (0.00 sec) mysql> mysql>

"COALESCE(value,...)" 對比操做符,返回第一個非NULL的值，若是沒有非null值，則返回NULL

mysql> SELECT GREATEST(200,0); +-----------------+
| GREATEST(200,0) |
+-----------------+
|             200 |
+-----------------+
1 row in set (0.00 sec) mysql> mysql> SELECT GREATEST(18.0,3.1415926,5.2,1314.520); +---------------------------------------+
| GREATEST(18.0,3.1415926,5.2,1314.520) |
+---------------------------------------+
|                          1314.5200000 |
+---------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT GREATEST('B','A','C','D','E','F','G'); +---------------------------------------+
| GREATEST('B','A','C','D','E','F','G') |
+---------------------------------------+
| G                                     |
+---------------------------------------+
1 row in set (0.00 sec) mysql>

"GREATEST(value1,value2,...)" 返回其中最大的值

mysql> SELECT 5 IN (1,5,15,20,25); +---------------------+
| 5 IN (1,5,15,20,25) |
+---------------------+
|                   1 |
+---------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT 10 IN (1,5,15,20,25); +----------------------+
| 10 IN (1,5,15,20,25) |
+----------------------+
|                    0 |
+----------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT 'zhengjie' IN ('yinzhengjie'); +-------------------------------+
| 'zhengjie' IN ('yinzhengjie') |
+-------------------------------+
|                             0 |
+-------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT 'zhengjie' IN ('yinzhengjie','zhengjie'); +------------------------------------------+
| 'zhengjie' IN ('yinzhengjie','zhengjie') |
+------------------------------------------+
|                                        1 |
+------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT(20,30) IN ((10,20),(30,40)); +------------------------------+
| (20,30) IN ((10,20),(30,40)) |
+------------------------------+
|                            0 |
+------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT(20,30) IN ((10,20),(30,20)); +------------------------------+
| (20,30) IN ((10,20),(30,20)) |
+------------------------------+
|                            0 |
+------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT(20,30) IN ((10,20),(20,30)); +------------------------------+
| (20,30) IN ((10,20),(20,30)) |
+------------------------------+
|                            1 |
+------------------------------+
1 row in set (0.00 sec) mysql>

"expr IN (value,...)"對比操做符,當expr值能在values中找到，則返回1，不然返回0。"expr NOT IN (value,...)" 對比操做符與其相反

mysql> SELECT ISNULL(10*20); +---------------+
| ISNULL(10*20) |
+---------------+
|             0 |
+---------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT ISNULL(10/0); +--------------+
| ISNULL(10/0) |
+--------------+
|            1 |
+--------------+
1 row in set, 1 warning (0.00 sec) mysql> mysql>

"Isnull(expr)" 操做符,若是expr是null，則返回1，不然返回0

mysql> mysql> SELECT LEAST(10,20,30); +-----------------+
| LEAST(10,20,30) |
+-----------------+
|              10 |
+-----------------+
1 row in set (0.00 sec) mysql> mysql> SELECT LEAST(9.8,3.1415926,5.20); +---------------------------+
| LEAST(9.8,3.1415926,5.20) |
+---------------------------+
|                 3.1415926 |
+---------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT LEAST('D','C','A','F'); +------------------------+
| LEAST('D','C','A','F') |
+------------------------+
| A                      |
+------------------------+
1 row in set (0.00 sec) mysql>

LEAST(value1,value2,...),返回最小值，若是其中有值爲null，則返回null 

3>.邏輯操做符

　　邏輯操做符返回1（TRUE），0（FALSE），或者NULL。 

mysql> SELECT NOT 100; +---------+
| NOT 100 |
+---------+
|       0 |
+---------+
1 row in set (0.00 sec) mysql> mysql> SELECT NOT 0; +-------+
| NOT 0 |
+-------+
|     1 |
+-------+
1 row in set (0.00 sec) mysql> mysql> SELECT NOT NULL; +----------+
| NOT NULL |
+----------+
|     NULL |
+----------+
1 row in set (0.00 sec) mysql> mysql> SELECT !(10+20); +----------+
| !(10+20) |
+----------+
|        0 |
+----------+
1 row in set (0.00 sec) mysql> mysql> SELECT ! 10 + 12; +-----------+
| ! 10 + 12 |
+-----------+
|        12 |
+-----------+
1 row in set (0.00 sec) mysql> mysql> SELECT ! 10 + 1; +----------+
| ! 10 + 1 |
+----------+
|        1 |
+----------+
1 row in set (0.00 sec) mysql>

"NOT, !" 邏輯操做符表明非操做

mysql> SELECT 1 AND 1; +---------+
| 1 AND 1 |
+---------+
|       1 |
+---------+
1 row in set (0.00 sec) mysql> mysql> SELECT 1 AND 0; +---------+
| 1 AND 0 |
+---------+
|       0 |
+---------+
1 row in set (0.00 sec) mysql> mysql> SELECT 1 AND NULL; +------------+
| 1 AND NULL |
+------------+
|       NULL |
+------------+
1 row in set (0.00 sec) mysql> mysql> SELECT 0 AND NULL; +------------+
| 0 AND NULL |
+------------+
|          0 |
+------------+
1 row in set (0.00 sec) mysql> mysql> SELECT NULL AND 0; +------------+
| NULL AND 0 |
+------------+
|          0 |
+------------+
1 row in set (0.00 sec) mysql> mysql> SELECT NULL AND 1; +------------+
| NULL AND 1 |
+------------+
|       NULL |
+------------+
1 row in set (0.00 sec) mysql>

" And,&& "邏輯操做符

mysql> SELECT 2 OR 3; +--------+
| 2 OR 3 |
+--------+
|      1 |
+--------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT 2 OR 0; +--------+
| 2 OR 0 |
+--------+
|      1 |
+--------+
1 row in set (0.00 sec) mysql> mysql> SELECT 0 OR 0; +--------+
| 0 OR 0 |
+--------+
|      0 |
+--------+
1 row in set (0.00 sec) mysql> mysql> SELECT 0 OR NULL; +-----------+
| 0 OR NULL |
+-----------+
|      NULL |
+-----------+
1 row in set (0.00 sec) mysql> mysql> SELECT 1 OR NULL; +-----------+
| 1 OR NULL |
+-----------+
|         1 |
+-----------+
1 row in set (0.00 sec) mysql>

"OR, ||" 邏輯操做符

mysql> SELECT 2 XOR 3; +---------+
| 2 XOR 3 |
+---------+
|       0 |
+---------+
1 row in set (0.00 sec) mysql> mysql> SELECT 2 XOR 0; +---------+
| 2 XOR 0 |
+---------+
|       1 |
+---------+
1 row in set (0.00 sec) mysql> mysql> SELECT 2 XOR NULL; +------------+
| 2 XOR NULL |
+------------+
|       NULL |
+------------+
1 row in set (0.00 sec) mysql> mysql> SELECT 2 XOR 3 XOR 4; +---------------+
| 2 XOR 3 XOR 4 |
+---------------+
|             1 |
+---------------+
1 row in set (0.00 sec) mysql>

"Xor" 邏輯操做符

4>.分配操做符

　　所謂的分配操做符就是賦值操做。

mysql> SELECT @name,@age; #MySQL使用「@」來聲明一個變量 +-------+------+
| @name | @age |
+-------+------+
| NULL  | NULL |
+-------+------+
1 row in set (0.00 sec) mysql> mysql> SELECT @name:='yinzhengjie',@age:=18;       #MySQL使用":="來進行賦值操做 +----------------------+----------+
| @name:='yinzhengjie' | @age:=18 |
+----------------------+----------+
| yinzhengjie          |       18 |
+----------------------+----------+
1 row in set, 2 warnings (0.00 sec) mysql> mysql> SELECT @name,@age; +-------------+------+
| @name       | @age |
+-------------+------+
| yinzhengjie |   18 |
+-------------+------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT * FROM yinzhengjie.teacher; +----+-----------+-----------+
| id | name      | course_id |
+----+-----------+-----------+
|  1 | 謝霆鋒    |        11 |
|  2 | 周杰倫    |         1 |
|  3 | 蔡依林    |        13 |
|  4 | 楊冪      |         2 |
|  5 | 胡歌      |        12 |
|  6 | 劉德華    |         3 |
|  7 | 張學友    |        10 |
|  8 | 郭德綱    |         4 |
|  9 | 林俊杰    |         9 |
+----+-----------+-----------+
9 rows in set (0.00 sec) mysql> mysql> SELECT @lines:=COUNT(*) FROM yinzhengjie.teacher; +------------------+
| @lines:=COUNT(*) |
+------------------+
|                9 |
+------------------+
1 row in set, 1 warning (0.00 sec) mysql>

mysql> SELECT @name:='yinzhengjie',@age:=18; 　　　　　　　　　　　　　　#MySQL使用":="來進行賦值操做

mysql> CREATE TABLE students(id INT(11),name VARCHAR(30)); Query OK, 0 rows affected (0.01 sec) mysql> mysql> INSERT INTO students(id,name) VALUES(1,'jason'),(2,'jay'),(3,'lady Gaga'),(4,'G.E.M'),(5,'JJ lin'); Query OK, 5 rows affected (0.00 sec) Records: 5  Duplicates: 0  Warnings: 0 mysql> mysql> SELECT * FROM students; +------+-----------+
| id   | name      |
+------+-----------+
|    1 | jason     |
|    2 | jay       |
|    3 | lady Gaga |
|    4 | G.E.M     |
|    5 | JJ lin    |
+------+-----------+
5 rows in set (0.00 sec) mysql> mysql> UPDATE students SET name = 'yinzhengjie' WHERE id = @number:=1; Query OK, 1 row affected, 1 warning (0.01 sec) Rows matched: 1  Changed: 1  Warnings: 1 mysql> mysql> SELECT * FROM students; +------+-------------+
| id   | name        |
+------+-------------+
|    1 | yinzhengjie |
|    2 | jay         |
|    3 | lady Gaga   |
|    4 | G.E.M       |
|    5 | JJ lin      |
+------+-------------+
5 rows in set (0.00 sec) mysql> mysql> mysql> SELECT @number; +---------+
| @number |
+---------+
|       1 |
+---------+
1 row in set (0.00 sec) mysql

:=操做符也能夠用在update等語句

　　"=" 操做符在兩種狀況下會被認爲是賦值操做，而其餘狀況下會認 爲是對比操做符。

　　　　第一：在SET語句中，「=」操做符會被認爲是賦值操做；

　　　　第二：在「update」語句中的SET子句中，「=」操做符也會被認爲是賦值操做。

mysql> SELECT @QQ; +------+
| @QQ  |
+------+
| NULL |
+------+
1 row in set (0.00 sec) mysql> mysql> SET @QQ = 1053419035; Query OK, 0 rows affected (0.00 sec) mysql> mysql> SELECT @QQ; +------------+
| @QQ        |
+------------+
| 1053419035 |
+------------+
1 row in set (0.00 sec) mysql> mysql>

mysql> SET @QQ = 1053419035;

mysql> CREATE TABLE students(id INT(11),name VARCHAR(30)); Query OK, 0 rows affected (0.01 sec) mysql> mysql> INSERT INTO students(id,name) VALUES(1,'jason'),(2,'jay'),(3,'lady Gaga'),(4,'G.E.M'),(5,'JJ lin'); Query OK, 5 rows affected (0.00 sec) Records: 5  Duplicates: 0  Warnings: 0 mysql> mysql> SELECT * FROM students; +------+-----------+
| id   | name      |
+------+-----------+
|    1 | jason     |
|    2 | jay       |
|    3 | lady Gaga |
|    4 | G.E.M     |
|    5 | JJ lin    |
+------+-----------+
rows in set (0.00 sec) mysql> mysql> UPDATE students SET name = 'yinzhengjie' WHERE id = @number:=1; Query OK, 1 row affected, 1 warning (0.01 sec) Rows matched: 1  Changed: 1  Warnings: 1 mysql> mysql> SELECT * FROM students; +------+-------------+
| id   | name        |
+------+-------------+
|    1 | yinzhengjie |
|    2 | jay         |
|    3 | lady Gaga   |
|    4 | G.E.M       |
|    5 | JJ lin      |
+------+-------------+
rows in set (0.00 sec) mysql> mysql> mysql> SELECT @number; +---------+
| @number |
+---------+
|       1 |
+---------+
row in set (0.00 sec)

mysql> UPDATE students SET name = 'yinzhengjie' WHERE id = @number:=1;

 

二.常見的函數介紹 

1>.流程控制函數

mysql> ? CASE OPERATOR Name: 'CASE OPERATOR' Description: Syntax: CASE value WHEN [compare_value] THEN result [WHEN [compare_value] THEN result ...] [ELSE result] END

CASE WHEN [condition] THEN result [WHEN [condition] THEN result ...] [ELSE result] END The first CASE syntax returns the result for the first value=compare_value comparison that is true. The second syntax returns the result for the first condition that is true. If no comparison or condition is true, the result after ELSE is returned, or NULL if there is no ELSE part. *Note*: The syntax of the CASE expression described here differs slightly from that of the SQL CASE statement described in [HELP CASE statement], for
use inside stored programs. The CASE statement cannot have an ELSE NULL clause, and it is terminated with END CASE instead of END. The return type of a CASE expression result is the aggregated type of
all result values: o If all types are numeric, the aggregated type is also numeric: o If at least one argument is double precision, the result is double
    precision. o Otherwise, if at least one argument is DECIMAL, the result is
    DECIMAL. o Otherwise, the result is an integer type (with one exception): o If all integer types are all signed or all unsigned, the result is the same sign and the precision is the highest of all specified integer types (that is, TINYINT, SMALLINT, MEDIUMINT, INT, or BIGINT). o If there is a combination of signed and unsigned integer types, the result is signed and the precision may be higher. For example, if the types are signed INT and unsigned INT, the result is signed BIGINT. o The exception is unsigned BIGINT combined with any signed integer type. The result is DECIMAL with sufficient precision and scale 0. o If all types are BIT, the result is BIT. Otherwise, BIT arguments are treated similar to BIGINT. o If all types are YEAR, the result is YEAR. Otherwise, YEAR arguments are treated similar to INT. o If all types are character string (CHAR or VARCHAR), the result is
  VARCHAR with maximum length determined by the longest character length of the operands. o If all types are character or binary string, the result is VARBINARY. o SET and ENUM are treated similar to VARCHAR; the result is VARCHAR. o If all types are JSON, the result is JSON. o If all types are temporal, the result is temporal: o If all temporal types are DATE, TIME, or TIMESTAMP, the result is DATE, TIME, or TIMESTAMP, respectively. o Otherwise, for a mix of temporal types, the result is DATETIME. o If all types are GEOMETRY, the result is GEOMETRY. o If any type is BLOB, the result is BLOB. o For all other type combinations, the result is VARCHAR. o Literal NULL operands are ignored for type aggregation. URL: http://dev.mysql.com/doc/refman/8.0/en/control-flow-functions.html Examples: mysql> SELECT CASE 1 WHEN 1 THEN 'one'
    ->     WHEN 2 THEN 'two' ELSE 'more' END; -> 'one' mysql> SELECT CASE WHEN 1>0 THEN 'true' ELSE 'false' END; -> 'true' mysql> SELECT CASE BINARY 'B'
    ->     WHEN 'a' THEN 1 WHEN 'b' THEN 2 END; -> NULL mysql>

查看幫助信息（mysql> ? CASE OPERATOR）

CASE value WHEN [compare_value] THEN result [WHEN [compare_value] THEN result ...] [ELSE result] END 　　• 當value等於compare_value時，則返回result，不然返回else裏的result， 若是沒有else子句則返回null

mysql> SELECT CASE 100
    ->  WHEN 100 THEN '一百'
    ->  WHEN 200 THEN '二百'
    ->  ELSE '未知'
    -> END; +-----------------------------------------------------------------------------+
| CASE 100
 WHEN 100 THEN '一百'
 WHEN 200 THEN '二百'
 ELSE '未知'
END       |
+-----------------------------------------------------------------------------+
| 一百                                                                        |
+-----------------------------------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT CASE 300 WHEN 100 THEN '一百' WHEN 200 THEN '二百' ELSE '未知' END; +--------------------------------------------------------------------------+
| CASE 300 WHEN 100 THEN '一百' WHEN 200 THEN '二百' ELSE '未知' END       |
+--------------------------------------------------------------------------+
| 未知                                                                     |
+--------------------------------------------------------------------------+
1 row in set (0.01 sec) mysql>

mysql> SELECT CASE 300 WHEN 100 THEN '一百' WHEN 200 THEN '二百' ELSE '未知' END;

CASE WHEN [condition] THEN result [WHEN [condition] THEN result ...] [ELSE result] END • 當第一個condition知足時，則返回result，不然返回else裏的result，若是 沒有else子句時則返回null

mysql> SELECT CASE WHEN 100 > 20 THEN '真的' ELSE '假的' END; +----------------------------------------------------+
| CASE WHEN 100 > 20 THEN '真的' ELSE '假的' END     |
+----------------------------------------------------+
| 真的                                               |
+----------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT CASE WHEN 10 > 20 THEN 'TRUE' ELSE 'FALSE' END; +------------------------------------------------+
| CASE WHEN 10 > 20 THEN 'TRUE' ELSE 'FALSE' END |
+------------------------------------------------+
| FALSE                                          |
+------------------------------------------------+
1 row in set (0.00 sec) mysql>

mysql> SELECT CASE WHEN 100 > 20 THEN '真的' ELSE '假的' END;

IF(expr1,expr2,expr3) • 當expr1爲1/true時，則返回expr2，不然返回expr3

mysql> SELECT IF(10>5,"大於","小於"); +----------------------------+
| IF(10>5,"大於","小於")     |
+----------------------------+
| 大於                       |
+----------------------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT IF(10>5,"YES","NO"); +---------------------+
| IF(10>5,"YES","NO") |
+---------------------+
| YES                 |
+---------------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT IF(STRCMP('yinzhengjie','zhengjie'),"YES","NO"); +-------------------------------------------------+
| IF(STRCMP('yinzhengjie','zhengjie'),"YES","NO") |
+-------------------------------------------------+
| YES                                             |
+-------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT IF(STRCMP('zhengjie','yinzhengjie'),"YES","NO"); +-------------------------------------------------+
| IF(STRCMP('zhengjie','yinzhengjie'),"YES","NO") |
+-------------------------------------------------+
| YES                                             |
+-------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT IF(STRCMP('yinzhengjie','yinzhengjie'),"YES","NO"); +----------------------------------------------------+
| IF(STRCMP('yinzhengjie','yinzhengjie'),"YES","NO") |
+----------------------------------------------------+
| NO                                                 |
+----------------------------------------------------+
1 row in set (0.00 sec) mysql>

mysql> SELECT IF(10>5,"大於","小於");

IFNULL(expr1,expr2) • 當expr1爲非null時，則返回expr1，不然返回expr2

mysql> SELECT IFNULL(10,2); +--------------+
| IFNULL(10,2) |
+--------------+
|           10 |
+--------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT IFNULL(NULL,2); +----------------+
| IFNULL(NULL,2) |
+----------------+
|              2 |
+----------------+
1 row in set (0.00 sec) mysql> mysql> SELECT IFNULL(10/0,2); +----------------+
| IFNULL(10/0,2) |
+----------------+
|         2.0000 |
+----------------+
1 row in set, 1 warning (0.00 sec) mysql> mysql> SELECT IFNULL(10/0,'NULL'); +---------------------+
| IFNULL(10/0,'NULL') |
+---------------------+
| NULL                |
+---------------------+
1 row in set, 1 warning (0.00 sec) mysql>

mysql> SELECT IFNULL(10/0,'NULL');

NULLIF(expr1,expr2) 　　• 當expr1等於expr2時，則返回null，不然返回expr1

mysql> mysql> SELECT NULLIF('yinzhengjie','yinzhengjie'); +-------------------------------------+
| NULLIF('yinzhengjie','yinzhengjie') |
+-------------------------------------+
| NULL                                |
+-------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT NULLIF('yinzhengjie','zhengjie'); +----------------------------------+
| NULLIF('yinzhengjie','zhengjie') |
+----------------------------------+
| yinzhengjie                      |
+----------------------------------+
1 row in set (0.00 sec) mysql>

mysql> SELECT NULLIF('yinzhengjie','yinzhengjie');

2>.字符串函數

ASCII(str)返回str字符串中最左邊字符的ascii碼值，若是是空串則返回0，若是str是null則返回null

CHAR(N,...[USINGcharset_name])將括號中的N轉化成ascii碼對應的字符，返回這些字符組成的字符串，其中的null會被忽略

mysql> SELECT CHAR_LENGTH('yinzhengjie'); +----------------------------+
| CHAR_LENGTH('yinzhengjie') |
+----------------------------+
|                         11 |
+----------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT CHAR_LENGTH('MySQL'); +----------------------+
| CHAR_LENGTH('MySQL') |
+----------------------+
|                    5 |
+----------------------+
1 row in set (0.00 sec) mysql>

CHAR_LENGTH(str) 返回字符串的字符長度

mysql> SELECT CONCAT('yin','zheng','jie'); +-----------------------------+
| CONCAT('yin','zheng','jie') |
+-----------------------------+
| yinzhengjie                 |
+-----------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT CONCAT('My','NULL','SQL'); +---------------------------+
| CONCAT('My','NULL','SQL') |
+---------------------------+
| MyNULLSQL                 |
+---------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT CONCAT('My',NULL,'SQL'); +-------------------------+
| CONCAT('My',NULL,'SQL') |
+-------------------------+
| NULL                    |
+-------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT CONCAT(3,1415,926); +--------------------+
| CONCAT(3,1415,926) |
+--------------------+
| 31415926           |
+--------------------+
1 row in set (0.01 sec) mysql> mysql> SELECT CONCAT(3.1415926); +-------------------+
| CONCAT(3.1415926) |
+-------------------+
| 3.1415926         |
+-------------------+
1 row in set (0.00 sec) mysql>

CONCAT(str1,str2,...) 返回括號裏全部參數字符串鏈接在一塊兒，當其中有參數爲NULL時則返回 NULL

mysql> SELECT CONCAT_WS('-','First name','NULL','Last name'); +------------------------------------------------+
| CONCAT_WS('-','First name','NULL','Last name') |
+------------------------------------------------+
| First name-NULL-Last name                      |
+------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT CONCAT_WS('-','First name',NULL,'Last name'); +----------------------------------------------+
| CONCAT_WS('-','First name',NULL,'Last name') |
+----------------------------------------------+
| First name-Last name                         |
+----------------------------------------------+
1 row in set (0.00 sec) mysql>

CONCAT_WS(separator,str1,str2,...) 返回以第一個參數爲分隔符的鏈接後的一個字符串，當有參數爲NULL時則null 被忽略

INSERT(str,pos,len,newstr) 將str中從pos位置開始後的len個字符替換成newstr字符串

INSTR(str,substr) 返回str字符串中第一個出現substr字符串的位置

mysql> SELECT LEFT('yinzhengjie2019',3); +---------------------------+
| LEFT('yinzhengjie2019',3) |
+---------------------------+
| yin                       |
+---------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT LEFT('yinzhengjie2019',11); +----------------------------+
| LEFT('yinzhengjie2019',11) |
+----------------------------+
| yinzhengjie                |
+----------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT LEFT('yinzhengjie2019',15); +----------------------------+
| LEFT('yinzhengjie2019',15) |
+----------------------------+
| yinzhengjie2019            |
+----------------------------+
1 row in set (0.00 sec) mysql>

LEFT(str,len) 返回str字符串中從左邊開始的len個長度的字符

mysql> SELECT LENGTH('yinzhengjie'); +-----------------------+
| LENGTH('yinzhengjie') |
+-----------------------+
|                    11 |
+-----------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT LENGTH('2019'); +----------------+
| LENGTH('2019') |
+----------------+
|              4 |
+----------------+
1 row in set (0.00 sec) mysql> mysql> SELECT LENGTH('yinzhengjie2019'); +---------------------------+
| LENGTH('yinzhengjie2019') |
+---------------------------+
|                        15 |
+---------------------------+
1 row in set (0.00 sec) mysql> mysql>

LENGTH(str)返回str字符串的byte字節長度

mysql> SELECT LOAD_FILE('/yinzhengjie/backup/student.bak'); +--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| LOAD_FILE('/yinzhengjie/backup/student.bak')                                                                                                                                   |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| 1-"尹正傑" 2-"耿宇星" 3-"陳飛" 4-"彭興旭" 5-"李慧鵬" 6-"孟欣" 7-"鮮惠珊" 8-"陳勁" 9-"居彭陽" 10-"李嘉韻" 11-"石鬧鬧" 12-"肖風" 13-"劉曉江" |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT LOAD_FILE('/yinzhengjie/backup/teacher.bak'); +----------------------------------------------+
| LOAD_FILE('/yinzhengjie/backup/teacher.bak') |
+----------------------------------------------+
| 2周杰倫1                                     |
+----------------------------------------------+
1 row in set (0.00 sec) mysql>

LOAD_FILE(file_name) 讀取文件且返回文件內容爲字符串

mysql> SELECT LOCATE('yin','yinzhengjie'); +-----------------------------+
| LOCATE('yin','yinzhengjie') |
+-----------------------------+
|                           1 |
+-----------------------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT LOCATE('zheng','yinzhengjie'); +-------------------------------+
| LOCATE('zheng','yinzhengjie') |
+-------------------------------+
|                             4 |
+-------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT LOCATE('jie','yinzhengjie'); +-----------------------------+
| LOCATE('jie','yinzhengjie') |
+-----------------------------+
|                           9 |
+-----------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT LOCATE('2019','yinzhengjie'); +------------------------------+
| LOCATE('2019','yinzhengjie') |
+------------------------------+
|                            0 |
+------------------------------+
1 row in set (0.00 sec) mysql>

LOCATE(substr,str) 返回str字符串中第一次出現substr字符串的位置，若是沒有則返回"0"

mysql> SELECT LOCATE('e','yinzhengjie','1'); +-------------------------------+
| LOCATE('e','yinzhengjie','1') |
+-------------------------------+
|                             6 |
+-------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT LOCATE('E','yinzhengjie','1'); +-------------------------------+
| LOCATE('E','yinzhengjie','1') |
+-------------------------------+
|                             6 |
+-------------------------------+
1 row in set (0.00 sec) mysql> SELECT LOCATE('e','yinzhengjie','8'); +-------------------------------+
| LOCATE('e','yinzhengjie','8') |
+-------------------------------+
|                            11 |
+-------------------------------+
1 row in set (0.00 sec) mysql> SELECT LOCATE('E','yinzhengjie','8'); +-------------------------------+
| LOCATE('E','yinzhengjie','8') |
+-------------------------------+
|                            11 |
+-------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT LOCATE('A','yinzhengjie','8'); +-------------------------------+
| LOCATE('A','yinzhengjie','8') |
+-------------------------------+
|                             0 |
+-------------------------------+
1 row in set (0.00 sec) mysql>

LOCATE(substr,str,pos) 返回str字符串中從pos位置開始第一次出現substr字符串的位置，若是沒有則返回"0"

mysql> SET @name1 = 'yinzhengjie'; Query OK, 0 rows affected (0.00 sec) mysql> mysql> SET @name2 = BINARY 'YinZhengJie'; Query OK, 0 rows affected (0.00 sec) mysql> mysql> SELECT @name1,@name2; +-------------+-------------+
| @name1      | @name2      |
+-------------+-------------+
| yinzhengjie | YinZhengJie |
+-------------+-------------+
1 row in set (0.00 sec) mysql> mysql> SELECT  LOWER(@name1),LOWER(@name2),LOWER(CONVERT(@name2 USING utf8)); +---------------+---------------+-----------------------------------+
| LOWER(@name1) | LOWER(@name2) | LOWER(CONVERT(@name2 USING utf8)) |
+---------------+---------------+-----------------------------------+
| yinzhengjie   | YinZhengJie   | yinzhengjie                       |
+---------------+---------------+-----------------------------------+
1 row in set, 1 warning (0.00 sec) mysql> mysql>

LOWER(str) 返回將str字符串中全部字符變換成小寫後的字符串，但對二進制文本無效

mysql> SELECT LPAD('yinzhengjie',20,'-'); +----------------------------+
| LPAD('yinzhengjie',20,'-') |
+----------------------------+
| ---------yinzhengjie |
+----------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT LPAD('yinzhengjie',15,'-'); +----------------------------+
| LPAD('yinzhengjie',15,'-') |
+----------------------------+
| ----yinzhengjie |
+----------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT LPAD('yinzhengjie',11,'-'); +----------------------------+
| LPAD('yinzhengjie',11,'-') |
+----------------------------+
| yinzhengjie                |
+----------------------------+
1 row in set (0.00 sec) mysql> SELECT LPAD('yinzhengjie',3,'-'); +---------------------------+
| LPAD('yinzhengjie',3,'-') |
+---------------------------+
| yin                       |
+---------------------------+
1 row in set (0.00 sec) mysql> mysql>

LPAD(str,len,padstr) 將str的左邊補充爲padstr，直到補充成len長度的字符串並返回;若是str的長度 比len長，則返回str中最左邊開始的len長度的字符

mysql> mysql> SELECT LTRIM(' yinzhengjie '); +------------------------------------------------+
| LTRIM(' yinzhengjie ') |
+------------------------------------------------+
| yinzhengjie                                    |
+------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT LTRIM('2019 yinzhengjie '); +----------------------------------------------------+
| LTRIM('2019 yinzhengjie ') |
+----------------------------------------------------+
| 2019               yinzhengjie                     |
+----------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql>

LTRIM(str) 將str最左邊的空格去掉並返回

mysql> SELECT REPEAT(' yinzhengjie ',3); +-----------------------------------------+
| REPEAT(' yinzhengjie ',3)               |
+-----------------------------------------+
|  yinzhengjie  yinzhengjie  yinzhengjie  |
+-----------------------------------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT REPEAT(' yinzhengjie ',-1); +----------------------------+
| REPEAT(' yinzhengjie ',-1) |
+----------------------------+
|                            |
+----------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT REPEAT(' yinzhengjie ',0); +---------------------------+
| REPEAT(' yinzhengjie ',0) |
+---------------------------+
|                           |
+---------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT REPEAT(' yinzhengjie ',5); +-------------------------------------------------------------------+
| REPEAT(' yinzhengjie ',5)                                         |
+-------------------------------------------------------------------+
|  yinzhengjie  yinzhengjie  yinzhengjie  yinzhengjie  yinzhengjie  |
+-------------------------------------------------------------------+
1 row in set (0.00 sec) mysql>

REPEAT(str,count) 將str重複count並組合成字符串返回，若是count<1，則返回空串

mysql> SELECT REPLACE("www.yinzhengjie.org.cn",'i','I'); +-------------------------------------------+
| REPLACE("www.yinzhengjie.org.cn",'i','I') |
+-------------------------------------------+
| www.yInzhengjIe.org.cn                    |
+-------------------------------------------+
1 row in set (0.00 sec) mysql> mysql>

REPLACE(str,from_str,to_str) 將全部str字符串中匹配from_str子串的地方都替換成to_str子字符串

mysql> SELECT REVERSE('尹正傑'); +----------------------+
| REVERSE('尹正傑')    |
+----------------------+
| 傑正尹               |
+----------------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT REVERSE('yinzhengjie'); +------------------------+
| REVERSE('yinzhengjie') |
+------------------------+
| eijgnehzniy            |
+------------------------+
1 row in set (0.00 sec) mysql>

REVERSE(str) 將str字符串中的字符按照倒序組合並返回

mysql> mysql> SELECT RIGHT('yinzhengjie2019',4); +----------------------------+
| RIGHT('yinzhengjie2019',4) |
+----------------------------+
| 2019                       |
+----------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT RIGHT('yinzhengjie2019',7); +----------------------------+
| RIGHT('yinzhengjie2019',7) |
+----------------------------+
| jie2019                    |
+----------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT RIGHT('yinzhengjie2019',12); +-----------------------------+
| RIGHT('yinzhengjie2019',12) |
+-----------------------------+
| zhengjie2019                |
+-----------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT RIGHT('yinzhengjie2019',15); +-----------------------------+
| RIGHT('yinzhengjie2019',15) |
+-----------------------------+
| yinzhengjie2019             |
+-----------------------------+
1 row in set (0.00 sec) mysql>

RIGHT(str,len) 將str字符串中從右邊開始的len個字符返回

mysql> SELECT RPAD('yinzhengjie2019',20,'-'); +--------------------------------+
| RPAD('yinzhengjie2019',20,'-') |
+--------------------------------+
| yinzhengjie2019----- |
+--------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT RPAD('yinzhengjie2019',18,'-'); +--------------------------------+
| RPAD('yinzhengjie2019',18,'-') |
+--------------------------------+
| yinzhengjie2019--- |
+--------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT RPAD('yinzhengjie2019',15,'-'); +--------------------------------+
| RPAD('yinzhengjie2019',15,'-') |
+--------------------------------+
| yinzhengjie2019                |
+--------------------------------+
1 row in set (0.00 sec) mysql> SELECT RPAD('yinzhengjie2019',11,'-'); +--------------------------------+
| RPAD('yinzhengjie2019',11,'-') |
+--------------------------------+
| yinzhengjie                    |
+--------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT RPAD('yinzhengjie2019',3,'-'); +-------------------------------+
| RPAD('yinzhengjie2019',3,'-') |
+-------------------------------+
| yin                           |
+-------------------------------+
1 row in set (0.00 sec) mysql> mysql>

RPAD(str,len,padstr) 將字符串str從右邊開始補充爲padstr直到總體長度爲len，若是str的長度自己大 於len，則返回str中len長度的字符串

mysql> SELECT RTRIM('yinzhengjie '); +-----------------------------+
| RTRIM('yinzhengjie ') |
+-----------------------------+
| yinzhengjie                 |
+-----------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT RTRIM(' yinzhengjie '); +-----------------------------------+
| RTRIM(' yinzhengjie ') |
+-----------------------------------+
|       yinzhengjie                 |
+-----------------------------------+
1 row in set (0.00 sec) mysql>

RTRIM(str) 將字符串str右邊的空格去掉並返回

mysql> SELECT SPACE(1); +----------+
| SPACE(1) |
+----------+
|          |
+----------+
1 row in set (0.00 sec) mysql> mysql> SELECT SPACE(10); +------------+
| SPACE(10)  |
+------------+
|            |
+------------+
1 row in set (0.00 sec) mysql> mysql> SELECT SPACE(20); +----------------------+
| SPACE(20)            |
+----------------------+
|                      |
+----------------------+
1 row in set (0.00 sec) mysql> SELECT SPACE(30); +--------------------------------+
| SPACE(30)                      |
+--------------------------------+
|                                |
+--------------------------------+
1 row in set (0.00 sec) mysql>

SPACE(N) 返回N個長度的空格組成的空字符串

SUBSTR(str,pos), SUBSTR(str FROM pos), SUBSTR(str,pos,len), SUBSTR(str FROM pos FOR len) SUBSTRING(str,pos), SUBSTRING(str FROM pos),SUBSTRING(str,pos,len), SUBSTRING(str FROM pos FOR len) 　　• 若是沒有len參數，則返回從pos位置開始的str中的子字符串;若是有len參數，則從pos位置開始返回str中長度爲len的子字符串;若是pos爲負值，則表明pos從右邊開始數

mysql> mysql> SELECT SUBSTR('yinzhengjie2019',5); +-----------------------------+
| SUBSTR('yinzhengjie2019',5) |
+-----------------------------+
| hengjie2019                 |
+-----------------------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT SUBSTRING('yinzhengjie2019',5); +--------------------------------+
| SUBSTRING('yinzhengjie2019',5) |
+--------------------------------+
| hengjie2019                    |
+--------------------------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT SUBSTR('yinzhengjie2019' FROM 5); +----------------------------------+
| SUBSTR('yinzhengjie2019' FROM 5) |
+----------------------------------+
| hengjie2019                      |
+----------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT SUBSTRING('yinzhengjie2019' FROM 5); +-------------------------------------+
| SUBSTRING('yinzhengjie2019' FROM 5) |
+-------------------------------------+
| hengjie2019                         |
+-------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT SUBSTR('yinzhengjie2019',5,8); +-------------------------------+
| SUBSTR('yinzhengjie2019',5,8) |
+-------------------------------+
| hengjie2                      |
+-------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT SUBSTRING('yinzhengjie2019',5,8); +----------------------------------+
| SUBSTRING('yinzhengjie2019',5,8) |
+----------------------------------+
| hengjie2                         |
+----------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT SUBSTRING('yinzhengjie2019',-4); +---------------------------------+
| SUBSTRING('yinzhengjie2019',-4) |
+---------------------------------+
| 2019                            |
+---------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT SUBSTR('yinzhengjie2019',-4); +------------------------------+
| SUBSTR('yinzhengjie2019',-4) |
+------------------------------+
| 2019                         |
+------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT SUBSTR('yinzhengjie2019',-4,5); +--------------------------------+
| SUBSTR('yinzhengjie2019',-4,5) |
+--------------------------------+
| 2019                           |
+--------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT SUBSTR('yinzhengjie2019',-4,2); +--------------------------------+
| SUBSTR('yinzhengjie2019',-4,2) |
+--------------------------------+
| 20                             |
+--------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT SUBSTRING('yinzhengjie2019' FROM -12 FOR 8); +---------------------------------------------+
| SUBSTRING('yinzhengjie2019' FROM -12 FOR 8) |
+---------------------------------------------+
| zhengjie                                    |
+---------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT SUBSTR('yinzhengjie2019' FROM -12 FOR 8); +------------------------------------------+
| SUBSTR('yinzhengjie2019' FROM -12 FOR 8) |
+------------------------------------------+
| zhengjie                                 |
+------------------------------------------+
1 row in set (0.00 sec) mysql>

關於SUBSTR和SUBSTRING的案例展現

mysql> SELECT SUBSTRING_INDEX('www.yinzhengjie.org.cn','.',5); +-------------------------------------------------+
| SUBSTRING_INDEX('www.yinzhengjie.org.cn','.',5) |
+-------------------------------------------------+
| www.yinzhengjie.org.cn                          |
+-------------------------------------------------+
1 row in set (0.00 sec) mysql> SELECT SUBSTRING_INDEX('www.yinzhengjie.org.cn','.',3); +-------------------------------------------------+
| SUBSTRING_INDEX('www.yinzhengjie.org.cn','.',3) |
+-------------------------------------------------+
| www.yinzhengjie.org                             |
+-------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT SUBSTRING_INDEX('www.yinzhengjie.org.cn','.',1); +-------------------------------------------------+
| SUBSTRING_INDEX('www.yinzhengjie.org.cn','.',1) |
+-------------------------------------------------+
| www                                             |
+-------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT SUBSTRING_INDEX('www.yinzhengjie.org.cn','.',-1); +--------------------------------------------------+
| SUBSTRING_INDEX('www.yinzhengjie.org.cn','.',-1) |
+--------------------------------------------------+
| cn                                               |
+--------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT SUBSTRING_INDEX('www.yinzhengjie.org.cn','.',-3); +--------------------------------------------------+
| SUBSTRING_INDEX('www.yinzhengjie.org.cn','.',-3) |
+--------------------------------------------------+
| yinzhengjie.org.cn                               |
+--------------------------------------------------+
1 row in set (0.00 sec) mysql> SELECT SUBSTRING_INDEX('www.yinzhengjie.org.cn','.',-5); +--------------------------------------------------+
| SUBSTRING_INDEX('www.yinzhengjie.org.cn','.',-5) |
+--------------------------------------------------+
| www.yinzhengjie.org.cn                           |
+--------------------------------------------------+
1 row in set (0.00 sec) mysql>

SUBSTRING_INDEX(str,delim,count) 當count爲正數，則返回delim出如今str字符串中第count次以前的子字符串，若是是負數，則從右邊開始計算

mysql> SET @name = 'yinzhengjie'; Query OK, 0 rows affected (0.00 sec) mysql> mysql> SET @name2 = BINARY 'YinZhengJie'; Query OK, 0 rows affected (0.00 sec) mysql> mysql> SELECT @name,@name2; +-------------+-------------+
| @name       | @name2      |
+-------------+-------------+
| yinzhengjie | YinZhengJie |
+-------------+-------------+
1 row in set (0.00 sec) mysql> mysql> SELECT UPPER(@name),UPPER(@name2),UPPER(CONVERT(@name2 USING utf8)); +--------------+---------------+-----------------------------------+
| UPPER(@name) | UPPER(@name2) | UPPER(CONVERT(@name2 USING utf8)) |
+--------------+---------------+-----------------------------------+
| YINZHENGJIE  | YinZhengJie   | YINZHENGJIE                       |
+--------------+---------------+-----------------------------------+
1 row in set, 1 warning (0.00 sec) mysql>

UPPER(str) 返回將str字符串中全部字符轉換成大寫的字符串,但對二進制文本無效

3>.字符串對比函數

 　　用到的關鍵詞有LIKE，NOT LIKE，STRCMP()，通配符"%"表示匹配0個或多個字符。通配符"_"表示匹配1個字符。

mysql> SELECT 'yin_zheng_jie' LIKE 'yin%'; +-----------------------------+
| 'yin_zheng_jie' LIKE 'yin%' |
+-----------------------------+
|                           1 |
+-----------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT 'yin_zheng_jie' LIKE 'yin%'; +-----------------------------+
| 'yin_zheng_jie' LIKE 'yin%' |
+-----------------------------+
|                           1 |
+-----------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT 'yin_zheng_jie' LIKE 'yin\_'; +------------------------------+
| 'yin_zheng_jie' LIKE 'yin\_' |
+------------------------------+
|                            0 |
+------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT 'yin_zheng_jie' LIKE 'yin\_%'; +-------------------------------+
| 'yin_zheng_jie' LIKE 'yin\_%' |
+-------------------------------+
|                             1 |
+-------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT 'yin_' LIKE 'yin|_' ESCAPE '|'; #當匹配字符中有特殊字符時，能夠用「\」或者ESCAPE來指定特殊字符爲普通字符，也就是咱們常說當轉義。 +--------------------------------+
| 'yin_' LIKE 'yin|_' ESCAPE '|' |
+--------------------------------+
|                              1 |
+--------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT 'yin_' LIKE 'yin\_'; +---------------------+
| 'yin_' LIKE 'yin\_' |
+---------------------+
|                   1 |
+---------------------+
1 row in set (0.00 sec) mysql>

mysql> SELECT 'yin_' LIKE 'yin|_' ESCAPE '|';　　　　　　　　　　 #當匹配字符中有特殊字符時，能夠用「\」或者ESCAPE來指定特殊字符爲普通字符，也就是咱們常說當轉義。

expr NOT LIKE pat [ESCAPE 'escape_char'] 是上一個字符串對比函數的反義 STRCMP(expr1,expr2) 當expr1等於expr2時等於0，當expr1小於expr2時爲-1，反之爲1　　

mysql> mysql> SELECT STRCMP(1,2); +-------------+
| STRCMP(1,2) |
+-------------+
|          -1 |
+-------------+
1 row in set (0.00 sec) mysql> mysql> SELECT STRCMP(3,2); +-------------+
| STRCMP(3,2) |
+-------------+
|           1 |
+-------------+
1 row in set (0.00 sec) mysql> mysql> SELECT STRCMP('yinzhengjie','yinzhengjie2019'); +-----------------------------------------+
| STRCMP('yinzhengjie','yinzhengjie2019') |
+-----------------------------------------+
|                                      -1 |
+-----------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT STRCMP('yinzhengjie','yinzhengjie'); +-------------------------------------+
| STRCMP('yinzhengjie','yinzhengjie') |
+-------------------------------------+
|                                   0 |
+-------------------------------------+
1 row in set (0.00 sec) mysql>

mysql> SELECT STRCMP('yinzhengjie','yinzhengjie2019');

mysql> SET @s1 = _latin1 'x' COLLATE latin1_general_ci; Query OK, 0 rows affected (0.00 sec) mysql> mysql> SET @s2 = _latin1 'X' COLLATE latin1_general_ci; Query OK, 0 rows affected (0.00 sec) mysql> mysql> SET @s3 = _latin1 'x' COLLATE latin1_general_cs; Query OK, 0 rows affected (0.00 sec) mysql> mysql> SET @s4 = _latin1 'X' COLLATE latin1_general_cs; Query OK, 0 rows affected (0.00 sec) mysql> mysql> SELECT STRCMP(@s1, @s2), STRCMP(@s3, @s4); +------------------+------------------+
| STRCMP(@s1, @s2) | STRCMP(@s3, @s4) |
+------------------+------------------+
|                0 |                1 |
+------------------+------------------+
1 row in set (0.00 sec) mysql> mysql>

mysql> SELECT STRCMP(@s1, @s2), STRCMP(@s3, @s4);

4>.數字函數之算數操做符 

/和DIV的區別： /表明除法;div表明整數型除法，相除以後只取整數部分

mysql> SELECT  3/5; +--------+
| 3/5    |
+--------+
| 0.6000 |
+--------+
1 row in set (0.00 sec) mysql> SELECT 12345/(2-1-1); +---------------+
| 12345/(2-1-1) |
+---------------+
|          NULL |
+---------------+
1 row in set, 1 warning (0.00 sec) mysql> mysql> SELECT 5 DIV 2; +---------+
| 5 DIV 2 |
+---------+
|       2 |
+---------+
1 row in set (0.00 sec) mysql> mysql> SELECT  10/3; +--------+
| 10/3   |
+--------+
| 3.3333 |
+--------+
1 row in set (0.00 sec) mysql> mysql> SELECT  10 DIV 3; +----------+
| 10 DIV 3 |
+----------+
|        3 |
+----------+
1 row in set (0.00 sec) mysql>

案例展現

5>.數字函數

mysql> SELECT ABS(10); +---------+
| ABS(10) |
+---------+
|      10 |
+---------+
1 row in set (0.01 sec) mysql> mysql> SELECT ABS(-10); +----------+
| ABS(-10) |
+----------+
|       10 |
+----------+
1 row in set (0.00 sec) mysql> mysql> SELECT ABS(-200); +-----------+
| ABS(-200) |
+-----------+
|       200 |
+-----------+
1 row in set (0.00 sec) mysql>

ABS(X) 絕對值函數

mysql> SELECT CEILING(1.23); +---------------+
| CEILING(1.23) |
+---------------+
|             2 |
+---------------+
1 row in set (0.00 sec) mysql> mysql> SELECT CEILING(0.98); +---------------+
| CEILING(0.98) |
+---------------+
|             1 |
+---------------+
1 row in set (0.00 sec) mysql> mysql> SELECT CEILING(3.1415926); +--------------------+
| CEILING(3.1415926) |
+--------------------+
|                  4 |
+--------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT CEILING(9.8); +--------------+
| CEILING(9.8) |
+--------------+
|           10 |
+--------------+
1 row in set (0.00 sec) mysql>

CEILING(X)/CEIL(X) 返回>=X值的最小整數

mysql> SELECT FLOOR(3.14); +-------------+
| FLOOR(3.14) |
+-------------+
|           3 |
+-------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT FLOOR(-3.14); +--------------+
| FLOOR(-3.14) |
+--------------+
|           -4 |
+--------------+
1 row in set (0.00 sec) mysql> mysql> SELECT FLOOR(9.8); +------------+
| FLOOR(9.8) |
+------------+
|          9 |
+------------+
1 row in set (0.00 sec) mysql> mysql> SELECT FLOOR(-9.8); +-------------+
| FLOOR(-9.8) |
+-------------+
|         -10 |
+-------------+
1 row in set (0.00 sec) mysql>

FLOOR(X) 返回<=X值的最大整數

mysql> SELECT MOD(10,3); +-----------+
| MOD(10,3) |
+-----------+
|         1 |
+-----------+
1 row in set (0.00 sec) mysql> mysql> SELECT MOD(108,10); +-------------+
| MOD(108,10) |
+-------------+
|           8 |
+-------------+
1 row in set (0.00 sec) mysql> mysql> SELECT 268 % 8; +---------+
| 268 % 8 |
+---------+
|       4 |
+---------+
1 row in set (0.00 sec) mysql> SELECT 108 % 10; +----------+
| 108 % 10 |
+----------+
|        8 |
+----------+
1 row in set (0.00 sec) mysql> mysql> SELECT 10 % 3; +--------+
| 10 % 3 |
+--------+
|      1 |
+--------+
1 row in set (0.00 sec) mysql> mysql> SELECT 10 MOD 3; +----------+
| 10 MOD 3 |
+----------+
|        1 |
+----------+
1 row in set (0.00 sec) mysql> mysql> SELECT 108 MOD 10; +------------+
| 108 MOD 10 |
+------------+
|          8 |
+------------+
1 row in set (0.00 sec) mysql>

MOD(N,M), N % M, N MOD M 取餘數操做，返回二者相除以後剩下的餘數

mysql> SELECT FLOOR(10 + (RAND() * 10)); +---------------------------+
| FLOOR(10 + (RAND() * 10)) |
+---------------------------+
|                        10 |
+---------------------------+
1 row in set (0.00 sec) mysql> SELECT FLOOR(10 + (RAND() * 10)); +---------------------------+
| FLOOR(10 + (RAND() * 10)) |
+---------------------------+
|                        17 |
+---------------------------+
1 row in set (0.00 sec) mysql> SELECT FLOOR(10 + (RAND() * 10)); +---------------------------+
| FLOOR(10 + (RAND() * 10)) |
+---------------------------+
|                        13 |
+---------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT * FROM yinzhengjie.student ORDER BY rand() LIMIT 1; +----+-----------+------------+
| id | name      | teacher_id |
+----+-----------+------------+
|  2 | 尹正傑    |          1 |
+----+-----------+------------+
1 row in set (0.01 sec) mysql>

RAND([N]) 獲取0到1之間的隨機小數，好比當想獲取7~12之間的隨機整數是可使用

mysql> SELECT ROUND(9.8); +------------+
| ROUND(9.8) |
+------------+
|         10 |
+------------+
1 row in set (0.00 sec) mysql> mysql> SELECT ROUND(3.14); +-------------+
| ROUND(3.14) |
+-------------+
|           3 |
+-------------+
1 row in set (0.00 sec) mysql> mysql> SELECT ROUND(3.1415926,5); +--------------------+
| ROUND(3.1415926,5) |
+--------------------+
|            3.14159 |
+--------------------+
1 row in set (0.00 sec) mysql> SELECT ROUND(3.1415926,3); +--------------------+
| ROUND(3.1415926,3) |
+--------------------+
|              3.142 |
+--------------------+
1 row in set (0.00 sec) mysql>

ROUND(X), ROUND(X,D) 四捨五入爲D位個小數，當D參數不存在是，則默認爲0

mysql> SELECT TRUNCATE(3.1415926,5); +-----------------------+
| TRUNCATE(3.1415926,5) |
+-----------------------+
|               3.14159 |
+-----------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT TRUNCATE(3.1415926,2); +-----------------------+
| TRUNCATE(3.1415926,2) |
+-----------------------+
|                  3.14 |
+-----------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT TRUNCATE(-3.1415926,2); +------------------------+
| TRUNCATE(-3.1415926,2) |
+------------------------+
|                  -3.14 |
+------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT TRUNCATE(1314,-2); +-------------------+
| TRUNCATE(1314,-2) |
+-------------------+
|              1300 |
+-------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT TRUNCATE(1314,-3); +-------------------+
| TRUNCATE(1314,-3) |
+-------------------+
|              1000 |
+-------------------+
1 row in set (0.00 sec) mysql> SELECT TRUNCATE(1314,-1); +-------------------+
| TRUNCATE(1314,-1) |
+-------------------+
|              1310 |
+-------------------+
1 row in set (0.00 sec) mysql>

TRUNCATE(X,D) 數字X只保留D位的小數，其他均捨棄

6>.日期和時間函數

mysql> SELECT ADDDATE('2014-07-18',INTERVAL 31 DAY); +---------------------------------------+
| ADDDATE('2014-07-18',INTERVAL 31 DAY) |
+---------------------------------------+
| 2014-08-18                            |
+---------------------------------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT ADDDATE('2014-07-18',31); +--------------------------+
| ADDDATE('2014-07-18',31) |
+--------------------------+
| 2014-08-18               |
+--------------------------+
1 row in set (0.00 sec) mysql>

ADDDATE(date,INTERVAL expr unit), ADDDATE(expr,days) 當expr爲正數時則爲增長時間，爲負數時則爲減小時間 Unit參數能夠是任意時間單位

mysql> SELECT ADDTIME('2018-12-31 23:59:59.999999', '1 1:1:1.000002'); +---------------------------------------------------------+
| ADDTIME('2018-12-31 23:59:59.999999', '1 1:1:1.000002') |
+---------------------------------------------------------+
| 2019-01-02 01:01:01.000001                              |
+---------------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT ADDTIME('01:00:00.999999', '02:00:00.999998'); +-----------------------------------------------+
| ADDTIME('01:00:00.999999', '02:00:00.999998') |
+-----------------------------------------------+
| 03:00:01.999997                               |
+-----------------------------------------------+
1 row in set (0.00 sec) mysql>

ADDTIME(expr1,expr2) 將expr2的時間增長到expr1上

mysql> SELECT CONVERT_TZ('2004-01-01 12:00:00','+00:00','+10:00'); +-----------------------------------------------------+
| CONVERT_TZ('2004-01-01 12:00:00','+00:00','+10:00') |
+-----------------------------------------------------+
| 2004-01-01 22:00:00                                 |
+-----------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql>

CONVERT_TZ(dt,from_tz,to_tz) 將時間dt從from_tz這個時區轉換成to_tz這個時區並返回 

mysql> SELECT CURDATE(); +------------+
| CURDATE()  |
+------------+
| 2019-01-27 |
+------------+
1 row in set (0.00 sec) mysql> mysql> SELECT CURDATE() + 0; +---------------+
| CURDATE() + 0 |
+---------------+
|      20190127 |
+---------------+
1 row in set (0.00 sec) mysql> mysql> SELECT CURDATE() + 3; +---------------+
| CURDATE() + 3 |
+---------------+
|      20190130 |
+---------------+
1 row in set (0.00 sec) mysql>

CURDATE()， CURRENT_DATE, CURRENT_DATE() 返回以yyyy-mm-dd或者yyyymmdd格式的當前時間

mysql> SELECT CURTIME(); +-----------+
| CURTIME() |
+-----------+
| 23:50:57  |
+-----------+
1 row in set (0.00 sec) mysql> mysql> SELECT CURTIME() + 0; +---------------+
| CURTIME() + 0 |
+---------------+
|        235111 |
+---------------+
1 row in set (0.00 sec) mysql> mysql> SELECT CURTIME() + 3; +---------------+
| CURTIME() + 3 |
+---------------+
|        235117 |
+---------------+
1 row in set (0.00 sec) mysql>

CURTIME(),CURRENT_TIME,CURRENT_TIME() 按照hh:mm:ss或者hhmmss格式返回當前時間

mysql> SELECT NOW(); +---------------------+
| NOW()               |
+---------------------+
| 2019-01-27 23:52:56 |
+---------------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT NOW() + 0; +----------------+
| NOW() + 0      |
+----------------+
| 20190127235302 |
+----------------+
1 row in set (0.00 sec) mysql> mysql> SELECT NOW() + 3; +----------------+
| NOW() + 3      |
+----------------+
| 20190127235308 |
+----------------+
1 row in set (0.00 sec) mysql>

Now(), CURRENT_TIMESTAMP,CURRENT_TIMESTAMP() 返回當前的日期和時間，格式爲yyyy-mm-dd hh:mi:ss或者 yyyymmddhhmiss

mysql> SELECT DATE('2018-12-31 01:02:03'); +-----------------------------+
| DATE('2018-12-31 01:02:03') |
+-----------------------------+
| 2018-12-31                  |
+-----------------------------+
1 row in set (0.00 sec) mysql> mysql>

DATE(expr) 獲取expr中的日期

mysql> SELECT DATEDIFF('2007-12-31 23:59:59','2007-12-30'); +----------------------------------------------+
| DATEDIFF('2007-12-31 23:59:59','2007-12-30') |
+----------------------------------------------+
|                                            1 |
+----------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT DATEDIFF('2010-11-30 23:59:59','2010-12-31'); +----------------------------------------------+
| DATEDIFF('2010-11-30 23:59:59','2010-12-31') |
+----------------------------------------------+
|                                          -31 |
+----------------------------------------------+
1 row in set (0.00 sec) mysql>

DATEDIFF(expr1,expr2) 返回expr1和expr2之間的天數差別，忽略時分秒

mysql> SELECT DATE_ADD('2000-12-31 23:59:59',INTERVAL 1 SECOND); +---------------------------------------------------+
| DATE_ADD('2000-12-31 23:59:59',INTERVAL 1 SECOND) |
+---------------------------------------------------+
| 2001-01-01 00:00:00                               |
+---------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT DATE_ADD('2010-12-31 23:59:59',INTERVAL 1 DAY); +------------------------------------------------+
| DATE_ADD('2010-12-31 23:59:59',INTERVAL 1 DAY) |
+------------------------------------------------+
| 2011-01-01 23:59:59                            |
+------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT DATE_ADD('2100-12-31 23:59:59',INTERVAL '1:1' MINUTE_SECOND); +--------------------------------------------------------------+
| DATE_ADD('2100-12-31 23:59:59',INTERVAL '1:1' MINUTE_SECOND) |
+--------------------------------------------------------------+
| 2101-01-01 00:01:00                                          |
+--------------------------------------------------------------+
1 row in set (0.01 sec) mysql> SELECT DATE_SUB('2005-01-01 00:00:00',INTERVAL '1 1:1:1' DAY_SECOND); +---------------------------------------------------------------+
| DATE_SUB('2005-01-01 00:00:00',INTERVAL '1 1:1:1' DAY_SECOND) |
+---------------------------------------------------------------+
| 2004-12-30 22:58:59                                           |
+---------------------------------------------------------------+
1 row in set (0.00 sec) mysql> SELECT DATE_ADD('1900-01-01 00:00:00',INTERVAL '-1 10' DAY_HOUR); +-----------------------------------------------------------+
| DATE_ADD('1900-01-01 00:00:00',INTERVAL '-1 10' DAY_HOUR) |
+-----------------------------------------------------------+
| 1899-12-30 14:00:00                                       |
+-----------------------------------------------------------+
1 row in set (0.00 sec) mysql> SELECT DATE_SUB('1998-01-02', INTERVAL 31 DAY); +-----------------------------------------+
| DATE_SUB('1998-01-02', INTERVAL 31 DAY) |
+-----------------------------------------+
| 1997-12-02                              |
+-----------------------------------------+
1 row in set (0.00 sec) mysql> SELECT DATE_ADD('1992-12-31 23:59:59.000002',INTERVAL '1.999999' SECOND_MICROSECOND); +-------------------------------------------------------------------------------+
| DATE_ADD('1992-12-31 23:59:59.000002',INTERVAL '1.999999' SECOND_MICROSECOND) |
+-------------------------------------------------------------------------------+
| 1993-01-01 00:00:01.000001                                                    |
+-------------------------------------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT DATE_ADD('2009-01-30', INTERVAL 1 MONTH); +------------------------------------------+
| DATE_ADD('2009-01-30', INTERVAL 1 MONTH) |
+------------------------------------------+
| 2009-02-28                               |
+------------------------------------------+
1 row in set (0.00 sec) mysql>

DATE_ADD(date,INTERVAL expr unit), DATE_SUB(date,INTERVAL expr unit) 增長或者減小時間

mysql> SELECT DATE_FORMAT('20190127235308','%Y-%m-%D-%H-%i-%s'); +---------------------------------------------------+
| DATE_FORMAT('20190127235308','%Y-%m-%D-%H-%i-%s') |
+---------------------------------------------------+
| 2019-01-27th-23-53-08                             |
+---------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT DATE_FORMAT('20190127235308','%Y-%M-%D-%H-%m-%s'); +---------------------------------------------------+
| DATE_FORMAT('20190127235308','%Y-%M-%D-%H-%m-%s') |
+---------------------------------------------------+
| 2019-January-27th-23-01-08                        |
+---------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT DATE_FORMAT('2009-10-04 22:23:00', '%W %M %Y'); +------------------------------------------------+
| DATE_FORMAT('2009-10-04 22:23:00', '%W %M %Y') |
+------------------------------------------------+
| Sunday October 2009                            |
+------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT DATE_FORMAT('2009-10-04 22:23:00', '%W %M %Y'); +------------------------------------------------+
| DATE_FORMAT('2009-10-04 22:23:00', '%W %M %Y') |
+------------------------------------------------+
| Sunday October 2009                            |
+------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT DATE_FORMAT('2007-10-04 22:23:00', '%H:%i:%s'); +------------------------------------------------+
| DATE_FORMAT('2007-10-04 22:23:00', '%H:%i:%s') |
+------------------------------------------------+
| 22:23:00                                       |
+------------------------------------------------+
1 row in set (0.00 sec) mysql> SELECT DATE_FORMAT('1900-10-04 22:23:00','%D %y %a %d %m %b %j'); +-----------------------------------------------------------+
| DATE_FORMAT('1900-10-04 22:23:00','%D %y %a %d %m %b %j') |
+-----------------------------------------------------------+
| 4th 00 Thu 04 10 Oct 277                                  |
+-----------------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT DATE_FORMAT('1997-10-04 22:23:00','%H %k %I %r %T %S %w'); +-----------------------------------------------------------+
| DATE_FORMAT('1997-10-04 22:23:00','%H %k %I %r %T %S %w') |
+-----------------------------------------------------------+
| 22 22 10 10:23:00 PM 22:23:00 00 6                        |
+-----------------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT DATE_FORMAT('1999-01-01', '%X %V'); +------------------------------------+
| DATE_FORMAT('1999-01-01', '%X %V') |
+------------------------------------+
| 1998 52                            |
+------------------------------------+
1 row in set (0.01 sec) mysql>  SELECT DATE_FORMAT('2006-06-00', '%d'); +---------------------------------+
| DATE_FORMAT('2006-06-00', '%d') |
+---------------------------------+
| 00                              |
+---------------------------------+
1 row in set (0.00 sec) mysql>

DATE_FORMAT(date,format) 將date日期時間轉換成format格式

mysql> SELECT DAYOFMONTH('2019-01-30'); +--------------------------+
| DAYOFMONTH('2019-01-30') |
+--------------------------+
|                       30 |
+--------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT DAYOFMONTH('2007-02-03'); +--------------------------+
| DAYOFMONTH('2007-02-03') |
+--------------------------+
|                        3 |
+--------------------------+
1 row in set (0.00 sec) mysql> mysql>

DAY(date), DAYOFMONTH(date) 返回date中日期在當前月份中是第幾天

mysql> SELECT DAYNAME('2007-02-03'); +-----------------------+
| DAYNAME('2007-02-03') |
+-----------------------+
| Saturday              |
+-----------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT DAYNAME('2019-01-30'); +-----------------------+
| DAYNAME('2019-01-30') |
+-----------------------+
| Wednesday             |
+-----------------------+
1 row in set (0.00 sec) mysql>

DAYNAME(date) 返回date時間是星期幾

mysql> mysql> SELECT DAYOFWEEK('2019-10-31'); +-------------------------+
| DAYOFWEEK('2019-10-31') |
+-------------------------+
|                       5 |
+-------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT DAYOFWEEK('2019-01-30'); +-------------------------+
| DAYOFWEEK('2019-01-30') |
+-------------------------+
|                       4 |
+-------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT DAYOFWEEK('2007-02-03'); +-------------------------+
| DAYOFWEEK('2007-02-03') |
+-------------------------+
|                       7 |
+-------------------------+
1 row in set (0.00 sec) mysql>

DAYOFWEEK(date) 返回date時間是星期「幾」

mysql> SELECT DAYOFYEAR('2007-02-03'); +-------------------------+
| DAYOFYEAR('2007-02-03') |
+-------------------------+
|                      34 |
+-------------------------+
1 row in set (0.00 sec) mysql>

DAYOFYEAR(date) 返回date是一年中的第幾天，取值範圍在1~366

mysql> SELECT EXTRACT(YEAR FROM '2009-07-02'); +---------------------------------+
| EXTRACT(YEAR FROM '2009-07-02') |
+---------------------------------+
|                            2009 |
+---------------------------------+
1 row in set (0.00 sec) mysql> mysql> mysql> mysql> SELECT EXTRACT(YEAR FROM '2009-07-02'); +---------------------------------+
| EXTRACT(YEAR FROM '2009-07-02') |
+---------------------------------+
|                            2009 |
+---------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT EXTRACT(YEAR_MONTH FROM '2009-07-02 01:02:03'); +------------------------------------------------+
| EXTRACT(YEAR_MONTH FROM '2009-07-02 01:02:03') |
+------------------------------------------------+
|                                         200907 |
+------------------------------------------------+
1 row in set (0.00 sec) mysql> SELECT EXTRACT(DAY_MINUTE FROM '2009-07-02 01:02:03'); +------------------------------------------------+
| EXTRACT(DAY_MINUTE FROM '2009-07-02 01:02:03') |
+------------------------------------------------+
|                                          20102 |
+------------------------------------------------+
1 row in set (0.00 sec) mysql> SELECT EXTRACT(MICROSECOND FROM '2003-01-02 10:30:00.000123'); +--------------------------------------------------------+
| EXTRACT(MICROSECOND FROM '2003-01-02 10:30:00.000123') |
+--------------------------------------------------------+
|                                                    123 |
+--------------------------------------------------------+
1 row in set (0.00 sec) mysql>

EXTRACT(unit FROM date) Unit單元和date_add/date_sub函數中的同樣，是獲取date日期的unit部分

mysql> SELECT FROM_UNIXTIME(1447430881); +---------------------------+
| FROM_UNIXTIME(1447430881) |
+---------------------------+
| 2015-11-13 11:08:01       |
+---------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT FROM_UNIXTIME(1447430881) + 0; +-------------------------------+
| FROM_UNIXTIME(1447430881) + 0 |
+-------------------------------+
|                20151113110801 |
+-------------------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT FROM_UNIXTIME(UNIX_TIMESTAMP(),'%Y %D %M %h:%i:%s %x'); +--------------------------------------------------------+
| FROM_UNIXTIME(UNIX_TIMESTAMP(),'%Y %D %M %h:%i:%s %x') |
+--------------------------------------------------------+
| 2019 28th January 12:12:06 2019                        |
+--------------------------------------------------------+
1 row in set (0.00 sec) mysql> mysql>

FROM_UNIXTIME(unix_timestamp), FROM_UNIXTIME(unix_timestamp,format) 根據給定的unixtime，返回yyyy-mm-ddhh:mi:ss或者yyyymmddhhmiss格式的具體時間，或者按照format返回時間

mysql> SELECT LAST_DAY('2004-02-05'); +------------------------+
| LAST_DAY('2004-02-05') |
+------------------------+
| 2004-02-29             |
+------------------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT LAST_DAY('2004-03-05'); +------------------------+
| LAST_DAY('2004-03-05') |
+------------------------+
| 2004-03-31             |
+------------------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT LAST_DAY('2004-03-45'); +------------------------+
| LAST_DAY('2004-03-45') |
+------------------------+
| NULL                   |
+------------------------+
1 row in set, 1 warning (0.00 sec) mysql>

LAST_DAY(date) 返回date日期所在月份的最後一天日期

mysql> SELECT NOW(), SLEEP(2), NOW(); +---------------------+----------+---------------------+
| NOW()               | SLEEP(2) | NOW()               |
+---------------------+----------+---------------------+
| 2019-01-28 00:14:36 |        0 | 2019-01-28 00:14:36 |
+---------------------+----------+---------------------+
1 row in set (2.00 sec) mysql> mysql> SELECT SYSDATE(), SLEEP(2), SYSDATE(); +---------------------+----------+---------------------+
| SYSDATE()           | SLEEP(2) | SYSDATE()           |
+---------------------+----------+---------------------+
| 2019-01-28 00:14:46 |        0 | 2019-01-28 00:14:48 |
+---------------------+----------+---------------------+
1 row in set (2.00 sec) mysql>

SYSDATE() 返回當前日期和時間，格式爲yyyy-mm-dd hh:mi:ss或者yyyymmddhhmiss 和now()函數的區別在於now()返回的時間是語句執行的時間，而sysdate()返回的 時間是該函數執行的時間

mysql> SELECT TIME('2003-12-31 01:02:03'); +-----------------------------+
| TIME('2003-12-31 01:02:03') |
+-----------------------------+
| 01:02:03                    |
+-----------------------------+
1 row in set (0.00 sec) mysql> mysql> mysql> SELECT TIME('2003-12-31 01:02:03.000123'); +------------------------------------+
| TIME('2003-12-31 01:02:03.000123') |
+------------------------------------+
| 01:02:03.000123                    |
+------------------------------------+
1 row in set (0.00 sec) mysql>

TIME(expr) 返回expr日期時間中的時間部分

mysql> SELECT UNIX_TIMESTAMP(); +------------------+
| UNIX_TIMESTAMP() |
+------------------+
|       1548652588 |
+------------------+
1 row in set (0.00 sec) mysql> mysql> mysql> mysql> SELECT UNIX_TIMESTAMP('2015-11-13 10:20:19'); +---------------------------------------+
| UNIX_TIMESTAMP('2015-11-13 10:20:19') |
+---------------------------------------+
|                            1447428019 |
+---------------------------------------+
1 row in set (0.00 sec) mysql>

UNIX_TIMESTAMP(), UNIX_TIMESTAMP(date) 若是沒有date參數，則返回當前時間到1970-01-01 00:00:00之間的秒數， 若是有date參數，則表示date到1970-01-01 00:00:00之間的秒數

7>.格式轉換函數

Cast()和convert()兩個函數均可以用來轉換數據類型或者轉換字符集容許轉換的數據類型包括: 
　　• Binary[N] • char[N] • Date • Datetime • decimal[M,[D]] • Time • Signed [integer] • Unsigned [integer]

mysql> SELECT CONVERT(_latin1'Müller' USING utf8); +---------------------------------------+
| CONVERT(_latin1'Müller' USING utf8)  |
+---------------------------------------+
| Müller                              |
+---------------------------------------+
1 row in set, 1 warning (0.00 sec) mysql>

mysql> SELECT CONVERT(_latin1'Müller' USING utf8);

mysql> SELECT CONVERT('test', CHAR CHARACTER SET utf8); +------------------------------------------+
| CONVERT('test', CHAR CHARACTER SET utf8) |
+------------------------------------------+
| test                                     |
+------------------------------------------+
1 row in set, 1 warning (0.00 sec) mysql>

mysql> SELECT CONVERT('test', CHAR CHARACTER SET utf8);

mysql> SELECT CAST('test' AS CHAR CHARACTER SET utf8); +-----------------------------------------+
| CAST('test' AS CHAR CHARACTER SET utf8) |
+-----------------------------------------+
| test                                    |
+-----------------------------------------+
1 row in set, 1 warning (0.00 sec) mysql>

mysql> SELECT CAST('test' AS CHAR CHARACTER SET utf8);

mysql> SELECT CAST('2019-01-01' AS DATE); +----------------------------+
| CAST('2019-01-01' AS DATE) |
+----------------------------+
| 2019-01-01                 |
+----------------------------+
1 row in set (0.00 sec) mysql> mysql>

mysql> SELECT CAST('2019-01-01' AS DATE);

mysql> SELECT CONVERT('2019-01-01', DATE); +-----------------------------+
| CONVERT('2019-01-01', DATE) |
+-----------------------------+
| 2019-01-01                  |
+-----------------------------+
1 row in set (0.01 sec) mysql>

mysql> SELECT CONVERT('2019-01-01', DATE);

8>.聚合函數

 　　聚合函數一般用在存在GROUP BY子句的語句中。

mysql> USE yinzhengjie; Database changed mysql> mysql> CREATE TABLE score_graph( -> id INT(11) PRIMARY KEY AUTO_INCREMENT, -> name VARCHAR(30), -> subject VARCHAR(30), -> score INT(3) -> ); Query OK, 0 rows affected (0.02 sec) mysql> mysql> mysql> INSERT INTO score_graph(name,subject,score) VALUES('尹正傑','英語',120); Query OK, 1 row affected (0.00 sec) mysql> INSERT INTO score_graph(name,subject,score) VALUES('尹正傑','語文',118); Query OK, 1 row affected (0.00 sec) mysql> mysql> INSERT INTO score_graph(name,subject,score) VALUES('尹正傑','數學',120); Query OK, 1 row affected (0.01 sec) mysql> mysql> INSERT INTO score_graph(name,subject,score) VALUES('尹正傑','物理',110); Query OK, 1 row affected (0.01 sec) mysql> INSERT INTO score_graph(name,subject,score) VALUES('尹正傑','化學',112); Query OK, 1 row affected (0.00 sec) mysql> INSERT INTO score_graph(name,subject,score) VALUES('尹正傑','生物',108); Query OK, 1 row affected (0.00 sec) mysql> mysql> INSERT INTO score_graph(name,subject,score) VALUES('jason','語文',120); Query OK, 1 row affected (0.01 sec) mysql> INSERT INTO score_graph(name,subject,score) VALUES('jason','英語',110); Query OK, 1 row affected (0.00 sec) mysql> INSERT INTO score_graph(name,subject,score) VALUES('jason','數學',115); Query OK, 1 row affected (0.00 sec) mysql> INSERT INTO score_graph(name,subject,score) VALUES('jason','物理',105); Query OK, 1 row affected (0.00 sec) mysql> INSERT INTO score_graph(name,subject,score) VALUES('jason','化學',102); Query OK, 1 row affected (0.00 sec) mysql> mysql> INSERT INTO score_graph(name,subject,score) VALUES('jason','生物',98); Query OK, 1 row affected (0.01 sec) mysql> mysql> INSERT INTO score_graph(name,subject,score) VALUES('耿宇星','語文',116); Query OK, 1 row affected (0.00 sec) mysql> INSERT INTO score_graph(name,subject,score) VALUES('耿宇星','數學',112); Query OK, 1 row affected (0.00 sec) mysql> INSERT INTO score_graph(name,subject,score) VALUES('耿宇星','英語',101); Query OK, 1 row affected (0.00 sec) mysql> INSERT INTO score_graph(name,subject,score) VALUES('耿宇星','物理',103); Query OK, 1 row affected (0.00 sec) mysql> INSERT INTO score_graph(name,subject,score) VALUES('耿宇星','化學',112); Query OK, 1 row affected (0.01 sec) mysql> INSERT INTO score_graph(name,subject,score) VALUES('耿宇星','生物',78); Query OK, 1 row affected (0.00 sec) mysql> mysql> SELECT * FROM score_graph; +----+-----------+---------+-------+
| id | name      | subject | score |
+----+-----------+---------+-------+
|  1 | 尹正傑    | 英語    |   120 |
|  2 | 尹正傑    | 語文    |   118 |
|  3 | 尹正傑    | 數學    |   120 |
|  4 | 尹正傑    | 物理    |   110 |
|  5 | 尹正傑    | 化學    |   112 |
|  6 | 尹正傑    | 生物    |   108 |
|  7 | jason     | 語文    |   120 |
|  8 | jason     | 英語    |   110 |
|  9 | jason     | 數學    |   115 |
| 10 | jason     | 物理    |   105 |
| 11 | jason     | 化學    |   102 |
| 12 | jason     | 生物    |    98 |
| 13 | 耿宇星    | 語文    |   116 |
| 14 | 耿宇星    | 數學    |   112 |
| 15 | 耿宇星    | 英語    |   101 |
| 16 | 耿宇星    | 物理    |   103 |
| 17 | 耿宇星    | 化學    |   112 |
| 18 | 耿宇星    | 生物    |    78 |
+----+-----------+---------+-------+
18 rows in set (0.00 sec) mysql>

建立測試數據（mysql> CREATE TABLE score_graph( id INT(11) PRIMARY KEY AUTO_INCREMENT, name VARCHAR(30), subject VARCHAR(30), score INT(3) );）

mysql> SELECT * FROM score_graph; +----+-----------+---------+-------+
| id | name      | subject | score |
+----+-----------+---------+-------+
|  1 | 尹正傑    | 英語    |   120 |
|  2 | 尹正傑    | 語文    |   118 |
|  3 | 尹正傑    | 數學    |   120 |
|  4 | 尹正傑    | 物理    |   110 |
|  5 | 尹正傑    | 化學    |   112 |
|  6 | 尹正傑    | 生物    |   108 |
|  7 | jason     | 語文    |   120 |
|  8 | jason     | 英語    |   110 |
|  9 | jason     | 數學    |   115 |
| 10 | jason     | 物理    |   105 |
| 11 | jason     | 化學    |   102 |
| 12 | jason     | 生物    |    98 |
| 13 | 耿宇星    | 語文    |   116 |
| 14 | 耿宇星    | 數學    |   112 |
| 15 | 耿宇星    | 英語    |   101 |
| 16 | 耿宇星    | 物理    |   103 |
| 17 | 耿宇星    | 化學    |   112 |
| 18 | 耿宇星    | 生物    |    78 |
+----+-----------+---------+-------+
18 rows in set (0.01 sec) mysql> mysql> SELECT name,AVG(score) FROM score_graph GROUP BY name; +-----------+------------+
| name      | AVG(score) |
+-----------+------------+
| 尹正傑    |   114.6667 |
| jason     |   108.3333 |
| 耿宇星    |   103.6667 |
+-----------+------------+
3 rows in set (0.00 sec) mysql> mysql>

AVG([DISTINCT] expr) 計算expr的平均值，distinct關鍵詞表示是否排除重複值

mysql> SELECT * FROM score_graph; +----+-----------+---------+-------+
| id | name      | subject | score |
+----+-----------+---------+-------+
|  1 | 尹正傑    | 英語    |   120 |
|  2 | 尹正傑    | 語文    |   118 |
|  3 | 尹正傑    | 數學    |   120 |
|  4 | 尹正傑    | 物理    |   110 |
|  5 | 尹正傑    | 化學    |   112 |
|  6 | 尹正傑    | 生物    |   108 |
|  7 | jason     | 語文    |   120 |
|  8 | jason     | 英語    |   110 |
|  9 | jason     | 數學    |   115 |
| 10 | jason     | 物理    |   105 |
| 11 | jason     | 化學    |   102 |
| 12 | jason     | 生物    |    98 |
| 13 | 耿宇星    | 語文    |   116 |
| 14 | 耿宇星    | 數學    |   112 |
| 15 | 耿宇星    | 英語    |   101 |
| 16 | 耿宇星    | 物理    |   103 |
| 17 | 耿宇星    | 化學    |   112 |
| 18 | 耿宇星    | 生物    |    78 |
+----+-----------+---------+-------+
18 rows in set (0.00 sec) mysql> mysql> SELECT name,COUNT(*) FROM score_graph GROUP BY name; +-----------+----------+
| name      | COUNT(*) |
+-----------+----------+
| 尹正傑    |        6 |
| jason     |        6 |
| 耿宇星    |        6 |
+-----------+----------+
3 rows in set (0.00 sec) mysql> mysql>

COUNT(expr) 計算expr中的個數，若是沒有匹配則返回0，注意NULL的區別

mysql> SELECT * FROM score_graph; +----+-----------+---------+-------+
| id | name      | subject | score |
+----+-----------+---------+-------+
|  1 | 尹正傑    | 英語    |   120 |
|  2 | 尹正傑    | 語文    |   118 |
|  3 | 尹正傑    | 數學    |   120 |
|  4 | 尹正傑    | 物理    |   110 |
|  5 | 尹正傑    | 化學    |   112 |
|  6 | 尹正傑    | 生物    |   108 |
|  7 | jason     | 語文    |   120 |
|  8 | jason     | 英語    |   110 |
|  9 | jason     | 數學    |   115 |
| 10 | jason     | 物理    |   105 |
| 11 | jason     | 化學    |   102 |
| 12 | jason     | 生物    |    98 |
| 13 | 耿宇星    | 語文    |   116 |
| 14 | 耿宇星    | 數學    |   112 |
| 15 | 耿宇星    | 英語    |   101 |
| 16 | 耿宇星    | 物理    |   103 |
| 17 | 耿宇星    | 化學    |   112 |
| 18 | 耿宇星    | 生物    |    78 |
+----+-----------+---------+-------+
18 rows in set (0.00 sec) mysql> mysql> SELECT COUNT(DISTINCT id) FROM score_graph; +--------------------+
| COUNT(DISTINCT id) |
+--------------------+
|                 18 |
+--------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT COUNT(DISTINCT name) FROM score_graph; +----------------------+
| COUNT(DISTINCT name) |
+----------------------+
|                    3 |
+----------------------+
1 row in set (0.00 sec) mysql> mysql> SELECT COUNT(DISTINCT subject) FROM score_graph; +-------------------------+
| COUNT(DISTINCT subject) |
+-------------------------+
|                       6 |
+-------------------------+
1 row in set (0.01 sec) mysql> mysql> SELECT COUNT(DISTINCT score) FROM score_graph;

COUNT(DISTINCT expr,[expr...]) 計算有多少個不重複的expr值，注意是計算非NULL的個數

mysql> SELECT * FROM score_graph; +----+-----------+---------+-------+
| id | name      | subject | score |
+----+-----------+---------+-------+
|  1 | 尹正傑    | 英語    |   120 |
|  2 | 尹正傑    | 語文    |   118 |
|  3 | 尹正傑    | 數學    |   120 |
|  4 | 尹正傑    | 物理    |   110 |
|  5 | 尹正傑    | 化學    |   112 |
|  6 | 尹正傑    | 生物    |   108 |
|  7 | jason     | 語文    |   120 |
|  8 | jason     | 英語    |   110 |
|  9 | jason     | 數學    |   115 |
| 10 | jason     | 物理    |   105 |
| 11 | jason     | 化學    |   102 |
| 12 | jason     | 生物    |    98 |
| 13 | 耿宇星    | 語文    |   116 |
| 14 | 耿宇星    | 數學    |   112 |
| 15 | 耿宇星    | 英語    |   101 |
| 16 | 耿宇星    | 物理    |   103 |
| 17 | 耿宇星    | 化學    |   112 |
| 18 | 耿宇星    | 生物    |    78 |
+----+-----------+---------+-------+
18 rows in set (0.00 sec) mysql> mysql> SELECT name,MIN(score),MAX(score) FROM score_graph GROUP BY name; +-----------+------------+------------+
| name      | MIN(score) | MAX(score) |
+-----------+------------+------------+
| 尹正傑    |        108 |        120 |
| jason     |         98 |        120 |
| 耿宇星    |         78 |        116 |
+-----------+------------+------------+
3 rows in set (0.00 sec) mysql> mysql>

MAX([DISTINCT] expr),MIN([DISTINCT] expr) 返回expr中最大或者最小的值

mysql> SELECT * FROM score_graph; +----+-----------+---------+-------+
| id | name      | subject | score |
+----+-----------+---------+-------+
|  1 | 尹正傑    | 英語    |   120 |
|  2 | 尹正傑    | 語文    |   118 |
|  3 | 尹正傑    | 數學    |   120 |
|  4 | 尹正傑    | 物理    |   110 |
|  5 | 尹正傑    | 化學    |   112 |
|  6 | 尹正傑    | 生物    |   108 |
|  7 | jason     | 語文    |   120 |
|  8 | jason     | 英語    |   110 |
|  9 | jason     | 數學    |   115 |
| 10 | jason     | 物理    |   105 |
| 11 | jason     | 化學    |   102 |
| 12 | jason     | 生物    |    98 |
| 13 | 耿宇星    | 語文    |   116 |
| 14 | 耿宇星    | 數學    |   112 |
| 15 | 耿宇星    | 英語    |   101 |
| 16 | 耿宇星    | 物理    |   103 |
| 17 | 耿宇星    | 化學    |   112 |
| 18 | 耿宇星    | 生物    |    78 |
+----+-----------+---------+-------+
18 rows in set (0.00 sec) mysql> mysql> SELECT name,SUM(score) FROM score_graph GROUP BY name; +-----------+------------+
| name      | SUM(score) |
+-----------+------------+
| 尹正傑    |        688 |
| jason     |        650 |
| 耿宇星    |        622 |
+-----------+------------+
3 rows in set (0.00 sec) mysql>

SUM([DISTINCT] expr) 返回expr的求和值