DML語句

DML 操做是指對數據庫中表記錄的操做，主要包括表記錄的插入（insert）、更新（update）、刪除（delete）和查詢（select），是開發人員平常使用最頻繁的操做。

插入記錄

表建立好後，就能夠往裏插入記錄了，插入記錄的基本語法以下

INSERT INTO tablename (field1, field2, .…, fieldn）VALUES (value1, value2, ..……, valuen);

向表 emp 中插入：ename 爲 zzx1，hiredate 爲 2000-01-01，sal 爲 2000，deptno 爲 1

mysql> desc emp;
+----------+---------------+------+-----+---------+-------+
| Field    | Type          | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| ename    | varchar(10)   | YES  |     | NULL    |       |
| hiredate | date          | YES  |     | NULL    |       |
| sal      | decimal(10,2) | YES  |     | NULL    |       |
| deptno   | int(2)        | YES  |     | NULL    |       |
+----------+---------------+------+-----+---------+-------+
4 rows in set (0.01 sec)

mysql> insert into emp(ename,hiredate,sal,deptno) values('zzx1','2000-01-01','2000',1);
Query OK, 1 row affected (0.01 sec)

也能夠不用指定字段名稱，可是 values 後面的順序應該和字段的排列順序一致

mysql> insert into emp values('lisa','2003-02-01','3000',2);
Query OK, 1 row affected (0.01 sec)

mysql> insert into emp values('bjguan','2004-04-02','4000',1);
Query OK, 1 row affected (0.01 sec)

只對表中的 ename 和 sal 字段顯式插入值

mysql> insert into emp(ename,sal) values('dony',1000);
Query OK, 1 row affected (0.01 sec)

查看實際插入的值

mysql> select * from emp;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx1   | 2000-01-01 | 2000.00 |      1 |
| lisa   | 2003-02-01 | 3000.00 |      2 |
| bjguan | 2004-04-02 | 4000.00 |      1 |
| dony   | NULL       | 1000.00 |   NULL |
+--------+------------+---------+--------+
4 rows in set (0.00 sec)

能夠一次性插入多條記錄，每條記錄之間用逗號分隔

INSERT INTO tablename (field1, field2, ..…, fieldn)
VALUES
(record1_value1, record1_value2, .…, record1_valuen),
(record2_value1, record2_value2, .…, record2_valuen),
...
(recordn_value1, recordn_value2, .…, recordn_valuen);

首先建立表 dept

mysql> create table dept(deptno int(2), deptname varchar(10));
Query OK, 0 rows affected (0.03 sec)

mysql> desc dept;
+----------+-------------+------+-----+---------+-------+
| Field    | Type        | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| deptno   | int(2)      | YES  |     | NULL    |       |
| deptname | varchar(10) | YES  |     | NULL    |       |
+----------+-------------+------+-----+---------+-------+
2 rows in set (0.01 sec)

對 dept 表一次插入多條記錄

mysql> insert into dept values(1,'tech'),(2,'sale'),(5,'fin'),(5,'dept5'),(6,'dept6');
Query OK, 5 rows affected (0.01 sec)
Records: 5  Duplicates: 0  Warnings: 0

mysql> select * from dept;
+--------+----------+
| deptno | deptname |
+--------+----------+
|      1 | tech     |
|      2 | sale     |
|      5 | fin      |
|      5 | dept5    |
|      6 | dept6    |
+--------+----------+
5 rows in set (0.00 sec)

更新記錄

UPDATE tablename SET field1=value1, field2=value2, ..., fieldn=valuen [WHERE CONDITION]

將表 emp 中 ename 爲 「lisa」 的薪水（sal）從 3000 改成 4000

mysql> update emp set sal=4000 where ename='lisa';
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from emp;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx1   | 2000-01-01 | 2000.00 |      1 |
| lisa   | 2003-02-01 | 4000.00 |      2 |
| bjguan | 2004-04-02 | 4000.00 |      1 |
| dony   | NULL       | 1000.00 |   NULL |
+--------+------------+---------+--------+
4 rows in set (0.00 sec)

update 命令能夠同時更新多個表中的數據

UPDATE t1, t2, ..., tn set t1.field1=expr1, t2.field2=expr2, ..., tn.fieldn=exprn [WHERE CONDITION]

同時更新表 emp 中的字段 sal 和表 dept 中的字段 deptname

mysql> select * from emp;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx1   | 2000-01-01 |  100.00 |      1 |
| lisa   | 2003-02-01 |  200.00 |      2 |
| bjguan | 2004-04-02 |  100.00 |      1 |
| dony   | 2005-02-05 | 2000.00 |      4 |
+--------+------------+---------+--------+
4 rows in set (0.00 sec)

mysql> select * from dept;
+--------+----------+
| deptno | deptname |
+--------+----------+
|      1 | tech     |
|      2 | sale     |
|      5 | fin      |
+--------+----------+
3 rows in set (0.00 sec)

mysql> update emp a, dept b set a.sal=a.sal*b.deptno, b.deptname=a.ename where a.deptno=b.deptno;
Query OK, 3 rows affected (0.01 sec)
Rows matched: 5  Changed: 3  Warnings: 0

mysql> select * from emp;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx1   | 2000-01-01 |  100.00 |      1 |
| lisa   | 2003-02-01 |  400.00 |      2 |
| bjguan | 2004-04-02 |  100.00 |      1 |
| dony   | 2005-02-05 | 2000.00 |      4 |
+--------+------------+---------+--------+
4 rows in set (0.00 sec)

mysql> select * from dept;
+--------+----------+
| deptno | deptname |
+--------+----------+
|      1 | zzx1     |
|      2 | lisa     |
|      5 | fin      |
+--------+----------+
3 rows in set (0.00 sec)

刪除記錄

DELETE FROM tablename [where CONDITION]

將 emp 中 ename 爲 「dony」 的記錄所有刪除

mysql> delete from emp where ename='dony';
Query OK, 1 row affected (0.01 sec)

mysql> select * from emp;
+--------+------------+--------+--------+
| ename  | hiredate   | sal    | deptno |
+--------+------------+--------+--------+
| zzx1   | 2000-01-01 | 100.00 |      1 |
| lisa   | 2003-02-01 | 400.00 |      2 |
| bjguan | 2004-04-02 | 100.00 |      1 |
+--------+------------+--------+--------+
3 rows in set (0.00 sec)

能夠一次刪除多個表的數據

DELETE t1, t2, ..., tn FROM t1, t2, ..., tn [WHERE CONDITION]

若是 from 後面的表名用別名，則 delete 後面也要用相應的別名，不然會提示語法錯誤

同時刪除表 emp 和 dept 中 deptno 爲 3 的記錄

mysql> select * from emp;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx1   | 2000-01-01 |  100.00 |      1 |
| lisa   | 2003-02-01 |  200.00 |      2 |
| bjguan | 2004-04-02 |  100.00 |      1 |
| bzshen | 2005-04-01 |  300.00 |      3 |
| dony   | 2005-02-05 | 2000.00 |      4 |
+--------+------------+---------+--------+
5 rows in set (0.00 sec)

mysql> select * from dept;
+--------+----------+
| deptno | deptname |
+--------+----------+
|      1 | tach     |
|      2 | sale     |
|      3 | hr       |
|      5 | fin      |
+--------+----------+
4 rows in set (0.00 sec)

mysql> delete a,b from emp a,dept b where a.deptno=b.deptno and a.deptno=3;
Query OK, 2 rows affected (0.01 sec)

mysql> select * from emp;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx1   | 2000-01-01 |  100.00 |      1 |
| lisa   | 2003-02-01 |  200.00 |      2 |
| bjguan | 2004-04-02 |  100.00 |      1 |
| dony   | 2005-02-05 | 2000.00 |      4 |
+--------+------------+---------+--------+
4 rows in set (0.00 sec)

mysql> select * from dept;
+--------+----------+
| deptno | deptname |
+--------+----------+
|      1 | tach     |
|      2 | sale     |
|      5 | fin      |
+--------+----------+
3 rows in set (0.00 sec)

查詢記錄

SELECT * FROM tablename [where CONDITION]

顯示 emp 表中的所有記錄

mysql> select * from emp;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx    | 2000-01-01 | 2000.00 |      1 |
| lisa   | 2003-02-01 | 4000.00 |      2 |
| bjguan | 2004-04-02 | 5000.00 |      1 |
+--------+------------+---------+--------+
3 rows in set (0.00 sec)

mysql> select ename,hiredate,sal,deptno from emp;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx    | 2000-01-01 | 2000.00 |      1 |
| lisa   | 2003-02-01 | 4000.00 |      2 |
| bjguan | 2004-04-02 | 5000.00 |      1 |
+--------+------------+---------+--------+
3 rows in set (0.00 sec)

查詢不重複的記錄

將表中的記錄去掉重複後顯示出來，能夠用distinct關鍵字來實現：

mysql> select ename,hiredate,sal,deptno from emp;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx    | 2000-01-01 | 2000.00 |      1 |
| lisa   | 2003-02-01 | 4000.00 |      2 |
| bjguan | 2004-04-02 | 5000.00 |      1 |
+--------+------------+---------+--------+
3 rows in set (0.00 sec)

mysql> select distinct deptno from emp;
+--------+
| deptno |
+--------+
|      1 |
|      2 |
+--------+
2 rows in set (0.00 sec)

條件查詢

查詢全部 deptno 爲 1 的記錄

mysql> select * from emp;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx    | 2000-01-01 | 2000.00 |      1 |
| lisa   | 2003-02-01 | 4000.00 |      2 |
| bjguan | 2004-04-02 | 5000.00 |      1 |
+--------+------------+---------+--------+
3 rows in set (0.00 sec)

mysql> select * from emp where deptno=1;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx    | 2000-01-01 | 2000.00 |      1 |
| bjguan | 2004-04-02 | 5000.00 |      1 |
+--------+------------+---------+--------+
2 rows in set (0.00 sec)

多字段查詢

mysql> select * from emp where deptno=1 and sal<3000;
+-------+------------+---------+--------+
| ename | hiredate   | sal     | deptno |
+-------+------------+---------+--------+
| zzx   | 2000-01-01 | 2000.00 |      1 |
+-------+------------+---------+--------+
1 row in set (0.00 sec)

排序和限制

SELECT * FROM tablename [WHERE CONDITION] [ORDER BY field1 [DESC | ASC], field2 [DESC | ASC], ..., fieldn [DESC | ASC]]

DESC：降序排列     ASC：升序排列

把 emp 表中的記錄按照工資高低進行顯示

mysql> select * from emp order by sal;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx    | 2000-01-01 | 2000.00 |      1 |
| dony   | 2005-02-05 | 2000.00 |      4 |
| lisa   | 2003-02-01 | 4000.00 |      2 |
| bjguan | 2004-04-02 | 5000.00 |      1 |
+--------+------------+---------+--------+
4 rows in set (0.00 sec)

若是排序字段的值同樣，則值相同的字段按照第二個排序字段進行排序，依次類推。若是隻有一個排序字段，則這些字段相同的記錄將會無序排列。

把 emp 表中的記錄按照部門編號 deptno 字段排序

mysql> select * from emp order by deptno;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx    | 2000-01-01 | 2000.00 |      1 |
| bjguan | 2004-04-02 | 5000.00 |      1 |
| lisa   | 2003-02-01 | 4000.00 |      2 |
| dony   | 2005-02-05 | 2000.00 |      4 |
+--------+------------+---------+--------+
4 rows in set (0.00 sec)

對於 deptno 相同的前兩條記錄，若是要按照工資由高到低排序，可使用如下命令

mysql> select * from emp order by deptno,sal desc;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| bjguan | 2004-04-02 | 5000.00 |      1 |
| zzx    | 2000-01-01 | 2000.00 |      1 |
| lisa   | 2003-02-01 | 4000.00 |      2 |
| dony   | 2005-02-05 | 2000.00 |      4 |
+--------+------------+---------+--------+
4 rows in set (0.00 sec)

對於排序後的記錄，若是但願只顯示一部分，而不是所有，這時，就可使用 LIMIT 關鍵字來實現

SELECT ... [LIMIT offset_start, row_count]

其中 offset_start 表示記錄的起始偏移量，row_count 表示顯示的行數。

在默認狀況下，起始偏移量爲 0，只須要寫記錄行數就能夠，這時，實際顯示的就是前 n 條記錄。例如，顯示 emp 表中按照 sal 排序後的前 3 條記錄：

mysql> select * from emp order by sal limit 3;
+-------+------------+---------+--------+
| ename | hiredate   | sal     | deptno |
+-------+------------+---------+--------+
| zzx   | 2000-01-01 | 2000.00 |      1 |
| dony  | 2005-02-05 | 2000.00 |      4 |
| lisa  | 2003-02-01 | 4000.00 |      2 |
+-------+------------+---------+--------+
3 rows in set (0.00 sec)

若是要顯示 emp 表中按照 sal 排序後從第二條記錄開始的 3 條記錄，可使用如下命令：

mysql> select * from emp order by sal limit 1,3;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| dony   | 2005-02-05 | 2000.00 |      4 |
| lisa   | 2003-02-01 | 4000.00 |      2 |
| bjguan | 2004-04-02 | 5000.00 |      1 |
+--------+------------+---------+--------+
3 rows in set (0.00 sec)

聚合

SELECT [field1, field2, ..., fieldn] fun_name
FROM tablename
[WHERE where_contition]
[GROUP BY field1, field2, ..., fieldn
WITH ROLLUP]]
[HAVING where_contition]

參數說明：

• fun_name 表示要作的聚合操做，也就是聚合函數，經常使用的有 sum（求和）、count（記數）、max（最大值）、min（最小值）、avg（平均值）。
• GROUP BY 關鍵字表示要進行分類聚合的字段，好比要按照部門分類統計員工數量，部門就應該寫在 group by 後面。
• WITH ROLLUP 是可選語法，代表是否對分類聚合後的結果進行再彙總。
• HAVING 關鍵字表示對分類後的結果再進行條件的過濾。

注意：having 和 where 的區別在於，having 是對聚合後的結果進行條件的過濾，而 where 是在聚合前就對記錄進行過濾，若是邏輯容許，儘量用 where 先過濾記錄，這樣由於結果集減少，將對聚合的效率大大提升，最後再根據邏輯看是否用 having 進行再過濾。

在 emp 表中統計公司人數

mysql> select count(1) from emp;
+----------+
| count(1) |
+----------+
|        4 |
+----------+
1 row in set (0.00 sec)

在此基礎上，要統計各個部門的人數

mysql> select deptno,count(1) from emp group by deptno;
+--------+----------+
| deptno | count(1) |
+--------+----------+
|      1 |        2 |
|      2 |        1 |
|      4 |        1 |
+--------+----------+
3 rows in set (0.00 sec)

更詳細一些，既要統計部門人數，又要統計總人數

mysql> select deptno,count(1) from emp group by deptno with rollup;
+--------+----------+
| deptno | count(1) |
+--------+----------+
|      1 |        2 |
|      2 |        1 |
|      4 |        1 |
|   NULL |        4 |
+--------+----------+
4 rows in set (0.00 sec)

統計人數大於 1 的部門

mysql> select deptno,count(1) from emp group by deptno having count(1)>1;
+--------+----------+
| deptno | count(1) |
+--------+----------+
|      1 |        2 |
+--------+----------+
1 row in set (0.00 sec)

統計公司全部員工薪水總額、最高和最低薪水

mysql> select * from emp;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx    | 2000-01-01 | 2000.00 |      1 |
| lisa   | 2003-02-01 | 4000.00 |      2 |
| bjguan | 2004-04-02 | 5000.00 |      1 |
| dony   | 2005-02-05 | 2000.00 |      4 |
+--------+------------+---------+--------+
4 rows in set (0.00 sec)

mysql> select sum(sal),max(sal),min(sal) from emp;
+----------+----------+----------+
| sum(sal) | max(sal) | min(sal) |
+----------+----------+----------+
| 13000.00 |  5000.00 |  2000.00 |
+----------+----------+----------+
1 row in set (0.00 sec)

錶鏈接

當須要同時顯示多個表中的字段時，就能夠用錶鏈接來實現這樣的功能。從大類上分，錶鏈接分爲內鏈接和外鏈接，它們之間的最主要區別是，內鏈接僅選出兩張表中互相匹配的記錄，而外鏈接會選出其餘不匹配的記錄。經常使用的是內鏈接。

查詢出全部僱員的名字和所在部門名稱，由於僱員名稱和部門分別存放在表 emp 和 dept 中，所以，須要使用錶鏈接來進行查詢

mysql> select * from emp;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx    | 2000-01-01 | 2000.00 |      1 |
| lisa   | 2003-02-01 | 4000.00 |      2 |
| bjguan | 2004-04-02 | 5000.00 |      1 |
| dony   | 2005-02-05 | 2000.00 |      4 |
+--------+------------+---------+--------+
4 rows in set (0.00 sec)

mysql> select * from dept;
+--------+----------+
| deptno | deptname |
+--------+----------+
|      1 | tach     |
|      2 | sale     |
|      5 | fin      |
+--------+----------+
3 rows in set (0.01 sec)

mysql> select ename,deptname from emp,dept where emp.deptno=dept.deptno;
+--------+----------+
| ename  | deptname |
+--------+----------+
| zzx    | tach     |
| bjguan | tach     |
| lisa   | sale     |
+--------+----------+
3 rows in set (0.00 sec)

外鏈接又分爲左鏈接和右鏈接：

• 左鏈接：包含全部的左邊表中的記錄甚至是右邊表中沒有和它匹配的記錄。
• 右鏈接：包含全部的右邊表中的記錄甚至是左邊表中沒有和它匹配的記錄。

查詢 emp 中全部用戶名和所在部門名稱

mysql> select * from emp;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx    | 2000-01-01 | 2000.00 |      1 |
| lisa   | 2003-02-01 | 4000.00 |      2 |
| bjguan | 2004-04-02 | 5000.00 |      1 |
| dony   | 2005-02-05 | 2000.00 |      4 |
+--------+------------+---------+--------+
4 rows in set (0.00 sec)

mysql> select * from dept;
+--------+----------+
| deptno | deptname |
+--------+----------+
|      1 | tach     |
|      2 | sale     |
|      5 | fin      |
+--------+----------+
3 rows in set (0.00 sec)

mysql> select ename,deptname from emp left join dept on emp.deptno=dept.deptno;
+--------+----------+
| ename  | deptname |
+--------+----------+
| zzx    | tach     |
| bjguan | tach     |
| lisa   | sale     |
| dony   | NULL     |
+--------+----------+
4 rows in set (0.00 sec)

右鏈接和左鏈接相似，二者之間能夠互相轉化，上面的例子能夠改寫爲以下的右鏈接

mysql> select ename,deptname from dept right join emp on dept.deptno=emp.deptno;
+--------+----------+
| ename  | deptname |
+--------+----------+
| zzx    | tach     |
| bjguan | tach     |
| lisa   | sale     |
| dony   | NULL     |
+--------+----------+
4 rows in set (0.00 sec)

子查詢

某些狀況下，當進行查詢的時候，須要的條件是另一個 select 語句的結果，這個時候，就要用到子查詢。用於子查詢的關鍵字主要包括 in、not in、=、!=、exists、not exists 等。

從 emp 表中查詢出全部部門在 dept 表中的全部記錄

mysql> select * from emp
    -> where deptno
    -> in(select deptno from dept);
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx    | 2000-01-01 | 2000.00 |      1 |
| bjguan | 2004-04-02 | 5000.00 |      1 |
| lisa   | 2003-02-01 | 4000.00 |      2 |
+--------+------------+---------+--------+
3 rows in set (0.00 sec)

若是子查詢記錄數惟一，還能夠用 = 代替 in

mysql> select * from emp
    -> where deptno = (select deptno from dept);
ERROR 1242 (21000): Subquery returns more than 1 row
mysql> select * from emp
    -> where deptno = (select deptno from dept limit 1);
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx    | 2000-01-01 | 2000.00 |      1 |
| bjguan | 2004-04-02 | 5000.00 |      1 |
+--------+------------+---------+--------+
2 rows in set (0.00 sec)

某些狀況下，子查詢能夠轉化爲錶鏈接

mysql> select * from emp where deptno in(select deptno from dept);
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx    | 2000-01-01 | 2000.00 |      1 |
| bjguan | 2004-04-02 | 5000.00 |      1 |
| lisa   | 2003-02-01 | 4000.00 |      2 |
+--------+------------+---------+--------+
3 rows in set (0.00 sec)

mysql> select emp.* from emp, dept where emp.deptno=dept.deptno;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx    | 2000-01-01 | 2000.00 |      1 |
| bjguan | 2004-04-02 | 5000.00 |      1 |
| lisa   | 2003-02-01 | 4000.00 |      2 |
+--------+------------+---------+--------+
3 rows in set (0.00 sec)

注意：子查詢和錶鏈接之間的轉換主要應用在兩個方面。

• MySQL 4.1 之前的版本不支持子查詢，須要用錶鏈接來實現子查詢的功能.
• 錶鏈接在不少狀況下用於優化子查詢。

記錄聯合

將兩個表的數據按照必定的查詢條件查詢出來後，將結果合併到一塊兒顯示出來，這個時候，就須要用 union 和 union all 關鍵字來實現這樣的功能

SELECT * FROM t1
UNION | UNION ALL
SELECT * FROM t2
...
UNION | UNION ALL
SELECT * FROM tn;

UNION 和 UNION ALL 的主要區別是 UNION ALL 是把結果集直接合並在一塊兒，而 UNION 是將 UNION ALL 後的結果進行一次 DISTINCT，去除重複記錄後的結果。

將 emp 和 dept 表中的部門編號的集合顯示出來

mysql> select * from emp;
+--------+------------+---------+--------+
| ename  | hiredate   | sal     | deptno |
+--------+------------+---------+--------+
| zzx    | 2000-01-01 | 2000.00 |      1 |
| lisa   | 2003-02-01 | 4000.00 |      2 |
| bjguan | 2004-04-02 | 5000.00 |      1 |
| dony   | 2005-02-05 | 2000.00 |      4 |
+--------+------------+---------+--------+
4 rows in set (0.00 sec)

mysql> select * from dept;
+--------+----------+
| deptno | deptname |
+--------+----------+
|      1 | tach     |
|      2 | sale     |
|      5 | fin      |
+--------+----------+
3 rows in set (0.00 sec)

mysql> select deptno from emp
    -> union all
    -> select deptno from dept;
+--------+
| deptno |
+--------+
|      1 |
|      2 |
|      1 |
|      4 |
|      1 |
|      2 |
|      5 |
+--------+
7 rows in set (0.00 sec)

將結果去掉重複記錄後顯示以下

mysql> select deptno from emp
    -> union
    -> select deptno from dept;
+--------+
| deptno |
+--------+
|      1 |
|      2 |
|      4 |
|      5 |
+--------+
4 rows in set (0.00 sec)