MySQL簡單查詢和單表查詢

MySQL記錄操做

概覽

MySQL數據操做： DML

在MySQL管理軟件中，能夠經過SQL語句中的DML語言來實現數據的操做，包括

1. 使用INSERT實現數據的插入
2. UPDATE實現數據的更新
3. 使用DELETE實現數據的刪除
4. 使用SELECT查詢數據以及。

插入數據insert

1. 插入完整數據（順序插入）
    語法一：
    INSERT INTO 表名(字段1,字段2,字段3…字段n) VALUES(值1,值2,值3…值n);

    語法二：
    INSERT INTO 表名 VALUES (值1,值2,值3…值n);

2. 指定字段插入數據
    語法：
    INSERT INTO 表名(字段1,字段2,字段3…) VALUES (值1,值2,值3…);

3. 插入多條記錄
    語法：
    INSERT INTO 表名 VALUES
        (值1,值2,值3…值n),
        (值1,值2,值3…值n),
        (值1,值2,值3…值n);
        
4. 插入查詢結果
    語法：
    INSERT INTO 表名(字段1,字段2,字段3…字段n) 
                    SELECT (字段1,字段2,字段3…字段n) FROM 表2
                    WHERE …;

更新數據update

語法：
    UPDATE 表名 SET
        字段1=值1,
        字段2=值2,
        WHERE CONDITION;

示例：
    UPDATE mysql.user SET password=password(‘123’) 
        where user=’root’ and host=’localhost’;

刪除數據delete

語法：
    DELETE FROM 表名 
        WHERE CONITION;

示例：
    DELETE FROM mysql.user 
        WHERE password=’’;

練習：
    更新MySQL root用戶密碼爲mysql123
    刪除除從本地登陸的root用戶之外的全部用戶

查詢數據 search

1.單表查詢

關鍵字執行的優先級:

from
where
group by
select
distinct
having
order by
limit

1.找到表:from

2.拿着where指定的約束條件，去文件/表中取出一條條記錄

3.將取出的一條條記錄進行分組group by，若是沒有group by，則總體做爲一組

4.執行select（去重）

5.將分組的結果進行having過濾

6.將結果按條件排序：order by

7.限制結果的顯示條數

簡單查詢

#建立表
create table employee(
id int not null unique auto_increment,
emp_name varchar(20) not null,
sex enum('male','female') not null default 'male', #大部分是男的
age int(3) unsigned not null default 28,
hire_date date not null,
post varchar(50),
post_comment varchar(100),
salary double(15,2),
office int, #一個部門一個屋子
depart_id int
);

#查看錶結構
mysql> desc employee;
+--------------+-----------------------+------+-----+---------+----------------+
| Field        | Type                  | Null | Key | Default | Extra          |
+--------------+-----------------------+------+-----+---------+----------------+
| id           | int(11)               | NO   | PRI | NULL    | auto_increment |
| emp_name     | varchar(20)           | NO   |     | NULL    |                |
| sex          | enum('male','female') | NO   |     | male    |                |
| age          | int(3) unsigned       | NO   |     | 28      |                |
| hire_date    | date                  | NO   |     | NULL    |                |
| post         | varchar(50)           | YES  |     | NULL    |                |
| post_comment | varchar(100)          | YES  |     | NULL    |                |
| salary       | double(15,2)          | YES  |     | NULL    |                |
| office       | int(11)               | YES  |     | NULL    |                |
| depart_id    | int(11)               | YES  |     | NULL    |                |
+--------------+-----------------------+------+-----+---------+----------------+


#插入記錄
#三個部門：教學，銷售，運營
insert into employee(emp_name,sex,age,hire_date,post,salary,office,depart_id) values
('egon','male',18,'20170301','辦事處',7300.33,401,1), #如下是教學部
('anwen','male',78,'20150302','teacher',1000000.31,401,1),
('wudi','male',81,'20130305','teacher',8300,401,1),
('yuanhao','male',73,'20140701','teacher',3500,401,1),
('liwen','male',28,'20121101','teacher',2100,401,1),
('jingliyang','female',18,'20110211','teacher',9000,401,1),
('jinxin','male',18,'19000301','teacher',30000,401,1),
('成龍','male',48,'20101111','teacher',10000,401,1),

('歪歪','female',48,'20150311','sale',3000.13,402,2),#如下是銷售部門
('丫丫','female',38,'20101101','sale',2000.35,402,2),
('丁丁','female',18,'20110312','sale',1000.37,402,2),
('星星','female',18,'20160513','sale',3000.29,402,2),
('格格','female',28,'20170127','sale',4000.33,402,2),

('張xx','male',28,'20160311','operation',10000.13,403,3), #如下是運營部門
('程咬金','male',18,'19970312','operation',20000,403,3),
('程咬銀','female',18,'20130311','operation',19000,403,3),
('程咬銅','male',18,'20150411','operation',18000,403,3),
('程咬鐵','female',18,'20140512','operation',17000,403,3)
;

#ps：若是在windows系統中，插入中文字符，select的結果爲空白，能夠將全部字符編碼統一設置成gbk

準備表和記錄

#簡單查詢
    SELECT id,emp_name,sex,age,hire_date,post,post_comment,salary,office,depart_id 
    FROM employee;

    SELECT * FROM employee;

    SELECT emp_name,salary FROM employee;

#避免重複DISTINCT
    SELECT DISTINCT post FROM employee;    

#經過四則運算查詢
    SELECT emp_name, salary*12 FROM employee;
    SELECT emp_name, salary*12 AS Annual_salary FROM employee;
    SELECT emp_name, salary*12 Annual_salary FROM employee;

#定義顯示格式
   CONCAT() 函數用於鏈接字符串
   SELECT CONCAT('姓名: ',emp_name,'  年薪: ', salary*12)  AS Annual_salary 
   FROM employee;
   
   CONCAT_WS() 第一個參數爲分隔符
   SELECT CONCAT_WS(':',emp_name,salary*12)  AS Annual_salary 
   FROM employee;

   結合CASE語句：
   SELECT
       (
           CASE
           WHEN emp_name = 'jingliyang' THEN
               emp_name
           WHEN emp_name = 'alex' THEN
               CONCAT(emp_name,'_BIGSB')
           ELSE
               concat(emp_name, 'SB')
           END
       ) as new_name
   FROM
       employee;

小練習：

1 查出全部員工的名字，薪資,格式爲
    <名字:egon>    <薪資:3000>
2 查出全部的崗位（去掉重複）
3 查出全部員工名字，以及他們的年薪,年薪的字段名爲annual_year

select concat('<名字:',emp_name,'>    ','<薪資:',salary,'>') from employee;
select distinct depart_id from employee;
select emp_name,salary*12 annual_salary from employee;

where約束

where字句中能夠使用：

1. 比較運算符：> < >= <= <> !=
2. between 80 and 100 值在80到100之間
3. in(80,90,100) 值是80或90或100
4. like 'e%'
       通配符能夠是%或_，
       %表示任意多字符
       _表示一個字符 
5. 邏輯運算符：在多個條件直接能夠使用邏輯運算符 and or not

#1:單條件查詢
    SELECT emp_name FROM employee
        WHERE post='sale';
        
#2:多條件查詢
    SELECT emp_name,salary FROM employee
        WHERE post='teacher' AND salary>10000;

#3:關鍵字BETWEEN AND
    SELECT emp_name,salary FROM employee 
        WHERE salary BETWEEN 10000 AND 20000;

    SELECT emp_name,salary FROM employee 
        WHERE salary NOT BETWEEN 10000 AND 20000;
    
#4:關鍵字IS NULL(判斷某個字段是否爲NULL不能用等號，須要用IS)
    SELECT emp_name,post_comment FROM employee 
        WHERE post_comment IS NULL;

    SELECT emp_name,post_comment FROM employee 
        WHERE post_comment IS NOT NULL;
        
    SELECT emp_name,post_comment FROM employee 
        WHERE post_comment=''; 注意''是空字符串，不是null
    ps：
        執行
        update employee set post_comment='' where id=2;
        再用上條查看，就會有結果了

#5:關鍵字IN集合查詢
    SELECT emp_name,salary FROM employee 
        WHERE salary=3000 OR salary=3500 OR salary=4000 OR salary=9000 ;
    
    SELECT emp_name,salary FROM employee 
        WHERE salary IN (3000,3500,4000,9000) ;

    SELECT emp_name,salary FROM employee 
        WHERE salary NOT IN (3000,3500,4000,9000) ;

#6:關鍵字LIKE模糊查詢
    通配符’%’
    SELECT * FROM employee 
            WHERE emp_name LIKE 'eg%';

    通配符’_’
    SELECT * FROM employee 
            WHERE emp_name LIKE 'al__';

小練習：

1. 查看崗位是teacher的員工姓名、年齡
2. 查看崗位是teacher且年齡大於30歲的員工姓名、年齡
3. 查看崗位是teacher且薪資在9000-1000範圍內的員工姓名、年齡、薪資
4. 查看崗位描述不爲NULL的員工信息
5. 查看崗位是teacher且薪資是10000或9000或30000的員工姓名、年齡、薪資
6. 查看崗位是teacher且薪資不是10000或9000或30000的員工姓名、年齡、薪資
7. 查看崗位是teacher且名字是jin開頭的員工姓名、年薪

select emp_name,age from employee where post = 'teacher';
select emp_name,age from employee where post='teacher' and age > 30; 
select emp_name,age,salary from employee where post='teacher' and salary between 9000 and 10000;
select * from employee where post_comment is not null;
select emp_name,age,salary from employee where post='teacher' and salary in (10000,9000,30000);
select emp_name,age,salary from employee where post='teacher' and salary not in (10000,9000,30000);
select emp_name,salary*12 from employee where post='teacher' and emp_name like 'jin%';

group by

單獨使用GROUP BY關鍵字分組
    SELECT post FROM employee GROUP BY post;
    注意：咱們按照post字段分組，那麼select查詢的字段只能是post，想要獲取組內的其餘相關信息，須要藉助函數

GROUP BY關鍵字和GROUP_CONCAT()函數一塊兒使用
    SELECT post,GROUP_CONCAT(emp_name) FROM employee GROUP BY post;#按照崗位分組，並查看組內成員名
    SELECT post,GROUP_CONCAT(emp_name) as emp_members FROM employee GROUP BY post;

GROUP BY與聚合函數一塊兒使用
    select post,count(id) as count from employee group by post;#按照崗位分組，並查看每一個組有多少人


強調：
若是咱們用unique的字段做爲分組的依據，則每一條記錄自成一組，這種分組沒有意義
多條記錄之間的某個字段值相同，該字段一般用來做爲分組的依據

聚合函數

#強調：聚合函數聚合的是組的內容，如果沒有分組，則默認一組

示例：
    SELECT COUNT(*) FROM employee;
    SELECT COUNT(*) FROM employee WHERE depart_id=1;
    SELECT MAX(salary) FROM employee;
    SELECT MIN(salary) FROM employee;
    SELECT AVG(salary) FROM employee;
    SELECT SUM(salary) FROM employee;
    SELECT SUM(salary) FROM employee WHERE depart_id=3;

小練習：

1. 查詢崗位名以及崗位包含的全部員工名字
2. 查詢崗位名以及各崗位內包含的員工個數
3. 查詢公司內男員工和女員工的個數
4. 查詢崗位名以及各崗位的平均薪資
5. 查詢崗位名以及各崗位的最高薪資
6. 查詢崗位名以及各崗位的最低薪資
7. 查詢男員工與男員工的平均薪資，女員工與女員工的平均薪資

#題1：分組
mysql> select post,group_concat(emp_name) from employee group by post;
#題目2：
mysql> select post,count(id) from employee group by post;
#題目3：
mysql> select sex,count(id) from employee group by sex;
#題目4：
mysql> select post,avg(salary) from employee group by post;
#題目5
mysql> select post,max(salary) from employee group by post;
#題目6
mysql> select post,min(salary) from employee group by post;
#題目七
mysql> select sex,avg(salary) from employee group by sex;

HAVING過濾

HAVING與WHERE不同的地方在於!!!!!!

#！！！執行優先級從高到低：where > group by > having 
#1. Where 發生在分組group by以前，於是Where中能夠有任意字段，可是絕對不能使用聚合函數。
#2. Having發生在分組group by以後，於是Having中能夠使用分組的字段，沒法直接取到其餘字段,能夠使用聚合函數

select * from emp where salary > 100000;

mysql> select post,group_concat(emp_name) from emp group by post having salary > 10000;#錯誤，分組後沒法直接取到salary字段
ERROR 1054 (42S22): Unknown column 'salary' in 'having clause'

mysql> select post,group_concat(emp_name) from emp group by post having avg(salary) > 10000;

小練習：

1. 查詢各崗位內包含的員工個數小於2的崗位名、崗位內包含員工名字、個數
3. 查詢各崗位平均薪資大於10000的崗位名、平均工資
4. 查詢各崗位平均薪資大於10000且小於20000的崗位名、平均工資

select post,group_concat(emp_name),count(id) from employee group by post having count(id) < 2;
select post,avg(salary) from employee group by post having avg(salary) > 10000;
select post,avg(salary) from employee group by post having avg(salary) > 10000 and avg(salary) <20000;

ORDER BY 查詢排序

按單列排序
    SELECT * FROM employee ORDER BY salary;
    SELECT * FROM employee ORDER BY salary ASC;
    SELECT * FROM employee ORDER BY salary DESC;

按多列排序:先按照age排序，若是年紀相同，則按照薪資排序
    SELECT * from employee
        ORDER BY age,
        salary DESC;

小練習：

1. 查詢全部員工信息，先按照age升序排序，若是age相同則按照hire_date降序排序
2. 查詢各崗位平均薪資大於10000的崗位名、平均工資,結果按平均薪資升序排列
3. 查詢各崗位平均薪資大於10000的崗位名、平均工資,結果按平均薪資降序排列

select * from employee ORDER BY age asc,hire_date desc;
select post,avg(salary) from employee group by post having avg(salary) > 10000 order by avg(salary) asc;
select post,avg(salary) from employee group by post having avg(salary) > 10000 order by avg(salary) desc;

LIMIT 限制查詢的記錄數

示例：
    SELECT * FROM employee ORDER BY salary DESC 
        LIMIT 3;                    #默認初始位置爲0 
    
    SELECT * FROM employee ORDER BY salary DESC
        LIMIT 0,5; #從第0開始，即先查詢出第一條，而後包含這一條在內日後查5條

    SELECT * FROM employee ORDER BY salary DESC
        LIMIT 5,5; #從第5開始，即先查詢出第6條，而後包含這一條在內日後查5條

小練習：

select * from  employee limit 0,5;
select * from  employee limit 5,5;
select * from  employee limit 10,5;

使用正則表達式查詢

SELECT * FROM employee WHERE emp_name REGEXP '^ale';

SELECT * FROM employee WHERE emp_name REGEXP 'on$';

SELECT * FROM employee WHERE emp_name REGEXP 'm{2}';


小結：對字符串匹配的方式
WHERE emp_name = 'egon';
WHERE emp_name LIKE 'yua%';
WHERE emp_name REGEXP 'on$';