MySQL实现单表查询的语句

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首先创建数据表

# 创建表    mysql> create table company.employee5(    id int primary key AUTO_INCREMENT not null,    name varchar(30) not null,    sex enum('male','female') default 'male' not null,    hire_date date not null,    post varchar(50) not null,    job_description varchar(100),    salary double(15,2) not null,    office int,    dep_id int    );    # 插入数据    mysql> insert into company.employee5(name,sex,hire_date,post,job_description,salary,office,dep_id) values     ('jack','male','20180202','instructor','teach',5000,501,100),    ('tom','male','20180203','instructor','teach',5500,501,100),    ('robin','male','20180202','instructor','teach',8000,501,100),    ('alice','female','20180202','instructor','teach',7200,501,100),    ('tianyun','male','20180202','hr','hrcc',600,502,101),    ('harry','male','20180202','hr',NULL,6000,502,101),    ('emma','female','20180206','sale','salecc',20000,503,102),    ('christine','female','20180205','sale','salecc',2200,503,102),    ('zhuzhu','male','20180205','sale',NULL,2200,503,102),    ('gougou','male','20180205','sale','',2200,503,102);    # 查看表结构    mysql> desc employee5;+-----------------+-----------------------+------+-----+---------+----------------+| Field           | Type                  | Null | Key | Default | Extra          |+-----------------+-----------------------+------+-----+---------+----------------+| id              | int(11)               | NO   | PRI | NULL    | auto_increment || name            | varchar(30)           | NO   |     | NULL    |                || sex             | enum('male','female') | NO   |     | male    |                || hire_date       | date                  | NO   |     | NULL    |                || post            | varchar(50)           | NO   |     | NULL    |                || job_description | varchar(100)          | YES  |     | NULL    |                || salary          | double(15,2)          | NO   |     | NULL    |                || office          | int(11)               | YES  |     | NULL    |                || dep_id          | int(11)               | YES  |     | NULL    |                |+-----------------+-----------------------+------+-----+---------+----------------+

查询语法

SELECT 字段1,字段2... FROM 表名                  WHERE 条件                  GROUP BY field                  HAVING 筛选                  ORDER BY field                  LIMIT 限制条数；

查看表中所有数据

mysql> select * from employee5;+----+-----------+--------+------------+------------+-----------------+----------+--------+--------+| id | name      | sex    | hire_date  | post       | job_description | salary   | office | dep_id |+----+-----------+--------+------------+------------+-----------------+----------+--------+--------+|  1 | jack      | male   | 2018-02-02 | instructor | teach           |  5000.00 |    501 |    100 ||  2 | tom       | male   | 2018-02-03 | instructor | teach           |  5500.00 |    501 |    100 ||  3 | robin     | male   | 2018-02-02 | instructor | teach           |  8000.00 |    501 |    100 ||  4 | alice     | female | 2018-02-02 | instructor | teach           |  7200.00 |    501 |    100 ||  5 | tianyun   | male   | 2018-02-02 | hr         | hrcc            |   600.00 |    502 |    101 ||  6 | harry     | male   | 2018-02-02 | hr         | NULL            |  6000.00 |    502 |    101 ||  7 | emma      | female | 2018-02-06 | sale       | salecc          | 20000.00 |    503 |    102 ||  8 | christine | female | 2018-02-05 | sale       | salecc          |  2200.00 |    503 |    102 ||  9 | zhuzhu    | male   | 2018-02-05 | sale       | NULL            |  2200.00 |    503 |    102 || 10 | gougou    | male   | 2018-02-05 | sale       |                 |  2200.00 |    503 |    102 |+----+-----------+--------+------------+------------+-----------------+----------+--------+--------+10 rows in set (0.00 sec)

简单查询

简单查询

mysql> SELECT * FROM employee5;mysql> SELECT name, salary, dep_id FROM employee5;

去重DISTINCT

mysql> SELECT post FROM employee5;mysql> SELECT DISTINCT post  FROM employee5;注：不能部分使用DISTINCT，通常仅用于某一字段。

通过四则运算查询

mysql> SELECT name, salary, salary*14 FROM employee5;mysql> SELECT name, salary, salary*14 AS Annual_salary FROM employee5;mysql> SELECT name, salary, salary*14 Annual_salary FROM employee5;

定义显示格式

CONCAT() 函数用于连接字符串mysql> SELECT CONCAT(name, ' annual salary: ', salary*14)  AS Annual_salary FROM employee5;

条件查询

a、语法    select * from 表名 where 条件    b、比较运算符    大于    小于    大于等于    小于等于    不等于    >        <        >=            <=            !=或<>c、逻辑运算符    并且    或者    非    and        or        notd、模糊查询    like    %           表示任意多个任意字符    _           表示一个任意字符e、范围查询    in                  表示在一个非连续的范围内    between...and...    表示在一个连续的范围内f、空判断    判断空：is null    判断非空：is not null g、优先级    小括号,not 比较运算符， 逻辑运算符    and比or优先级高，如果同时出现并希望先选or，需要结合()来使用

单条件查询

mysql> SELECT name,post FROM employee5 WHERE post='hr';

多条件查询

mysql> SELECT name,salary FROM employee5 WHERE post='hr' AND salary>5000;

关键字 BETWEEN AND查询

mysql> SELECT name,salary FROM employee5 WHERE salary BETWEEN 5000 AND 15000;mysql> SELECT name,salary FROM employee5 WHERE salary NOT BETWEEN 5000 AND 15000;

关键字 IS NULL 查询

mysql> SELECT name,job_description FROM employee5 WHERE job_description IS NULL;mysql> SELECT name,job_description FROM employee5 WHERE job_description IS NOT NULL;mysql> SELECT name,job_description FROM employee5 WHERE job_description='';

关键字IN集合查询

mysql> SELECT name, salary FROM employee5 WHERE salary=4000 OR salary=5000 OR salary=6000 OR salary=9000 ;mysql> SELECT name, salary FROM employee5 WHERE salary IN (4000,5000,6000,9000) ;mysql> SELECT name, salary FROM employee5 WHERE salary NOT IN (4000,5000,6000,9000) ;

关键字LIKE模糊查询

通配符'%'mysql> SELECT * FROM employee5 WHERE name LIKE 'al%';通配符'_'mysql> SELECT * FROM employee5 WHERE name LIKE 'al___';

查询排序

按单列排序

mysql> SELECT * FROM employee5 ORDER BY salary;mysql> SELECT name, salary FROM employee5 ORDER BY salary ASC;mysql> SELECT name, salary FROM employee5 ORDER BY salary DESC;

按多列排序

mysql> SELECT * FROM employee5 ORDER BY hire_date DESC,salary ASC;# 先按入职时间，再按薪水排序mysql> SELECT * FROM employee5 ORDER BY hire_date DESC, salary DESC;# 先按职位，再按薪水排序mysql> SELECT * FROM employee5 ORDER BY post, salary DESC;

分页查询 limit

mysql> SELECT * FROM employee5 ORDER BY salary DESC LIMIT 5;      //默认初始位置为0mysql> SELECT * FROM employee5 ORDER BY salary DESC LIMIT 0,5;mysql> SELECT * FROM employee5 ORDER BY salary DESC LIMIT 3,5;      //从第4条开始，共显示5条

聚合函数查询

    a、count(*)       表示计算总行数，括号中可以写*和列名    b、max(列)        表示求此列的最大值    c、min(列)        表示求此列的最小值    d、sun(列)        表示求此列的和    e、avg(列)        表示求此列的平均值    mysql> SELECT COUNT(*) FROM employee5;mysql> SELECT COUNT(*) FROM employee5 WHERE dep_id=101;mysql> SELECT MAX(salary) FROM employee5;mysql> SELECT MIN(salary) FROM employee5;mysql> SELECT AVG(salary) FROM employee5;mysql> SELECT SUM(salary) FROM employee5;mysql> SELECT SUM(salary) FROM employee5 WHERE dep_id=101;

分组查询

单独使用GROUP BY关键字分组mysql> SELECT post FROM employee5 GROUP BY post;注意：我们按照post字段分组，那么select查询的字段只能是post，想要获取组内的其他相关信息，需要借助函数

GROUP BY关键字和group_concat()函数一起使用

# 按照id分组，并查看组内成员mysql> SELECT dep_id,GROUP_CONCAT(name) FROM employee5 GROUP BY dep_id;mysql> SELECT dep_id,GROUP_CONCAT(name) as emp_members FROM employee5 GROUP BY dep_id;

GROUP BY和集合函数一起使用

# 按照dep_id 分组， 并计算组内成员工资总和mysql> SELECT dep_id,SUM(salary) FROM employee5 GROUP BY dep_id;# 按照dep_id分组，并计算组内成员工资平均值mysql> SELECT dep_id,AVG(salary) FROM employee5 GROUP BY dep_id;

正则表达式查询

mysql> SELECT * FROM employee5 WHERE name REGEXP '^j';mysql> SELECT * FROM employee5 WHERE salary REGEXP '[5]+.*';mysql> SELECT * FROM employee5 WHERE salary REGEXP '[5]{2}.*';

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