【MySQL】查询语法简介

2022-01-29 00:00:00 专区字符匹配大本营任意

前言：

本篇文章主要简介下MySQL中where,group by ,order by ,limit,join,union ,union all,子表等查询语法。

测试数据准备

create table emp (    empno numeric(4) not null,    ename varchar(10),    job varchar(9),    mgr numeric(4),    hiredate datetime,    sal numeric(7, 2),    comm numeric(7, 2),    deptno numeric(2));
create table dept (    deptno numeric(2),    dname varchar(14),    loc varchar(13));
create table salgrade (    grade numeric,    losal numeric,    hisal numeric);
insert into dept values (10, 'ACCOUNTING', 'NEW YORK');insert into dept values (20, 'RESEARCH', 'DALLAS');insert into dept values (30, 'SALES', 'CHICAGO');insert into dept values (40, 'OPERATIONS', 'BOSTON');
insert into salgrade values (1, 700, 1200);insert into salgrade values (2, 1201, 1400);insert into salgrade values (3, 1401, 2000);insert into salgrade values (4, 2001, 3000);insert into salgrade values (5, 3001, 9999);
insert into emp values (7369, 'SMITH', 'CLERK', 7902, '1980-12-17', 800, null, 20);insert into emp values (7499, 'ALLEN', 'SALESMAN', 7698, '1981-02-20', 1600, 300, 30);insert into emp values (7521, 'WARD', 'SALESMAN', 7698, '1981-02-22', 1250, 500, 30);insert into emp values (7566, 'JONES', 'MANAGER', 7839, '1981-04-02', 2975, null, 20);insert into emp values (7654, 'MARTIN', 'SALESMAN', 7698, '1981-09-28', 1250, 1400, 30);insert into emp values (7698, 'BLAKE', 'MANAGER', 7839, '1981-05-01', 2850, null, 30);insert into emp values (7782, 'CLARK', 'MANAGER', 7839, '1981-06-09', 2450, null, 10);insert into emp values (7788, 'SCOTT', 'ANALYST', 7566, '1982-12-09', 3000, null, 20);insert into emp values (7839, 'KING', 'PRESIDENT', null, '1981-11-17', 5000, null, 10);insert into emp values (7844, 'TURNER', 'SALESMAN', 7698, '1981-09-08', 1500, , 30);insert into emp values (7876, 'ADAMS', 'CLERK', 7788, '1983-01-12', 1100, null, 20);insert into emp values (7900, 'JAMES', 'CLERK', 7698, '1981-12-03', 950, null, 30);insert into emp values (7902, 'FORD', 'ANALYST', 7566, '1981-12-03', 3000, null, 20);insert into emp values (7934, 'MILLER', 'CLERK', 7782, '1982-01-23', 1300, null, 10);

1.模糊查询

mysql> select * from emp where ename like '%S%'; +-------+-------+---------+------+---------------------+---------+------+--------+| empno | ename | job     | mgr  | hiredate            | sal     | comm | deptno |+-------+-------+---------+------+---------------------+---------+------+--------+|  7369 | SMITH | CLERK   | 7902 | 1980-12-17 00:00:00 |  800.00 | NULL |     20 ||  7566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL |     20 ||  7788 | SCOTT | ANALYST | 7566 | 1982-12-09 00:00:00 | 3000.00 | NULL |     20 ||  7876 | ADAMS | CLERK   | 7788 | 1983-01-12 00:00:00 | 1100.00 | NULL |     20 ||  7900 | JAMES | CLERK   | 7698 | 1981-12-03 00:00:00 |  950.00 | NULL |     30 |+-------+-------+---------+------+---------------------+---------+------+--------+5 rows in set (.00 sec)
mysql> select * from emp where ename like 'S%'; +-------+-------+---------+------+---------------------+---------+------+--------+| empno | ename | job     | mgr  | hiredate            | sal     | comm | deptno |+-------+-------+---------+------+---------------------+---------+------+--------+|  7369 | SMITH | CLERK   | 7902 | 1980-12-17 00:00:00 |  800.00 | NULL |     20 ||  7788 | SCOTT | ANALYST | 7566 | 1982-12-09 00:00:00 | 3000.00 | NULL |     20 |+-------+-------+---------+------+---------------------+---------+------+--------+2 rows in set (0.01 sec)
mysql> select * from emp where ename like '%S';+-------+-------+---------+------+---------------------+---------+------+--------+| empno | ename | job     | mgr  | hiredate            | sal     | comm | deptno |+-------+-------+---------+------+---------------------+---------+------+--------+|  7566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL |     20 ||  7876 | ADAMS | CLERK   | 7788 | 1983-01-12 00:00:00 | 1100.00 | NULL |     20 ||  7900 | JAMES | CLERK   | 7698 | 1981-12-03 00:00:00 |  950.00 | NULL |     30 |+-------+-------+---------+------+---------------------+---------+------+--------+3 rows in set (0.00 sec)
mysql> select * from emp where ename like '_O%';+-------+-------+---------+------+---------------------+---------+------+--------+| empno | ename | job     | mgr  | hiredate            | sal     | comm | deptno |+-------+-------+---------+------+---------------------+---------+------+--------+|  7566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL |     20 ||  7902 | FORD  | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL |     20 |+-------+-------+---------+------+---------------------+---------+------+--------+2 rows in set (.00 sec)
总结：%表示任意个或多个字符，可匹配任意类型和长度的字符；_表示任意单个字符，匹配单个任意字符。

2.排序

mysql> select * from emp order by  sal;+-------+--------+-----------+------+---------------------+---------+---------+--------+| empno | ename  | job       | mgr  | hiredate            | sal     | comm    | deptno |+-------+--------+-----------+------+---------------------+---------+---------+--------+|  7369 | SMITH  | CLERK     | 7902 | 1980-12-17 00:00:00 |  800.00 |    NULL |     20 ||  7900 | JAMES  | CLERK     | 7698 | 1981-12-03 00:00:00 |  950.00 |    NULL |     30 ||  7876 | ADAMS  | CLERK     | 7788 | 1983-01-12 00:00:00 | 1100.00 |    NULL |     20 ||  7521 | WARD   | SALESMAN  | 7698 | 1981-02-22 00:00:00 | 1250.00 |  500.00 |     30 ||  7654 | MARTIN | SALESMAN  | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 |     30 ||  7934 | MILLER | CLERK     | 7782 | 1982-01-23 00:00:00 | 1300.00 |    NULL |     10 ||  7844 | TURNER | SALESMAN  | 7698 | 1981-09-08 00:00:00 | 1500.00 |    .00 |     30 ||  7499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 00:00:00 | 1600.00 |  300.00 |     30 ||  7782 | CLARK  | MANAGER   | 7839 | 1981-06-09 00:00:00 | 2450.00 |    NULL |     10 ||  7698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 00:00:00 | 2850.00 |    NULL |     30 ||  7566 | JONES  | MANAGER   | 7839 | 1981-04-02 00:00:00 | 2975.00 |    NULL |     20 ||  7788 | SCOTT  | ANALYST   | 7566 | 1982-12-09 00:00:00 | 3000.00 |    NULL |     20 ||  7902 | FORD   | ANALYST   | 7566 | 1981-12-03 00:00:00 | 3000.00 |    NULL |     20 ||  7839 | KING   | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 |    NULL |     10 |+-------+--------+-----------+------+---------------------+---------+---------+--------+14 rows in set (0.00 sec)
mysql> select * from emp order by  sal asc;+-------+--------+-----------+------+---------------------+---------+---------+--------+| empno | ename  | job       | mgr  | hiredate            | sal     | comm    | deptno |+-------+--------+-----------+------+---------------------+---------+---------+--------+|  7369 | SMITH  | CLERK     | 7902 | 1980-12-17 00:00:00 |  800.00 |    NULL |     20 ||  7900 | JAMES  | CLERK     | 7698 | 1981-12-03 00:00:00 |  950.00 |    NULL |     30 ||  7876 | ADAMS  | CLERK     | 7788 | 1983-01-12 00:00:00 | 1100.00 |    NULL |     20 ||  7521 | WARD   | SALESMAN  | 7698 | 1981-02-22 00:00:00 | 1250.00 |  500.00 |     30 ||  7654 | MARTIN | SALESMAN  | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 |     30 ||  7934 | MILLER | CLERK     | 7782 | 1982-01-23 00:00:00 | 1300.00 |    NULL |     10 ||  7844 | TURNER | SALESMAN  | 7698 | 1981-09-08 00:00:00 | 1500.00 |    0.00 |     30 ||  7499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 00:00:00 | 1600.00 |  300.00 |     30 ||  7782 | CLARK  | MANAGER   | 7839 | 1981-06-09 00:00:00 | 2450.00 |    NULL |     10 ||  7698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 00:00:00 | 2850.00 |    NULL |     30 ||  7566 | JONES  | MANAGER   | 7839 | 1981-04-02 00:00:00 | 2975.00 |    NULL |     20 ||  7788 | SCOTT  | ANALYST   | 7566 | 1982-12-09 00:00:00 | 3000.00 |    NULL |     20 ||  7902 | FORD   | ANALYST   | 7566 | 1981-12-03 00:00:00 | 3000.00 |    NULL |     20 ||  7839 | KING   | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 |    NULL |     10 |+-------+--------+-----------+------+---------------------+---------+---------+--------+14 rows in set (.00 sec)
mysql> select * from emp order by  sal desc;+-------+--------+-----------+------+---------------------+---------+---------+--------+| empno | ename  | job       | mgr  | hiredate            | sal     | comm    | deptno |+-------+--------+-----------+------+---------------------+---------+---------+--------+|  7839 | KING   | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 |    NULL |     10 ||  7788 | SCOTT  | ANALYST   | 7566 | 1982-12-09 00:00:00 | 3000.00 |    NULL |     20 ||  7902 | FORD   | ANALYST   | 7566 | 1981-12-03 00:00:00 | 3000.00 |    NULL |     20 ||  7566 | JONES  | MANAGER   | 7839 | 1981-04-02 00:00:00 | 2975.00 |    NULL |     20 ||  7698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 00:00:00 | 2850.00 |    NULL |     30 ||  7782 | CLARK  | MANAGER   | 7839 | 1981-06-09 00:00:00 | 2450.00 |    NULL |     10 ||  7499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 00:00:00 | 1600.00 |  300.00 |     30 ||  7844 | TURNER | SALESMAN  | 7698 | 1981-09-08 00:00:00 | 1500.00 |    0.00 |     30 ||  7934 | MILLER | CLERK     | 7782 | 1982-01-23 00:00:00 | 1300.00 |    NULL |     10 ||  7521 | WARD   | SALESMAN  | 7698 | 1981-02-22 00:00:00 | 1250.00 |  500.00 |     30 ||  7654 | MARTIN | SALESMAN  | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 |     30 ||  7876 | ADAMS  | CLERK     | 7788 | 1983-01-12 00:00:00 | 1100.00 |    NULL |     20 ||  7900 | JAMES  | CLERK     | 7698 | 1981-12-03 00:00:00 |  950.00 |    NULL |     30 ||  7369 | SMITH  | CLERK     | 7902 | 1980-12-17 00:00:00 |  800.00 |    NULL |     20 |+-------+--------+-----------+------+---------------------+---------+---------+--------+14 rows in set (0.00 sec)总结：order by排序默认按asc升序来排列也可指定desc降序排列

3.限制多少行

mysql> select * from emp limit  3;+-------+-------+----------+------+---------------------+---------+--------+--------+| empno | ename | job      | mgr  | hiredate            | sal     | comm   | deptno |+-------+-------+----------+------+---------------------+---------+--------+--------+|  7369 | SMITH | CLERK    | 7902 | 1980-12-17 00:00:00 |  800.00 |   NULL |     20 ||  7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 |     30 ||  7521 | WARD  | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 |     30 |+-------+-------+----------+------+---------------------+---------+--------+--------+3 rows in set (.00 sec)
mysql> select * from emp order by  sal desc limit  3;+-------+-------+-----------+------+---------------------+---------+------+--------+| empno | ename | job       | mgr  | hiredate            | sal     | comm | deptno |+-------+-------+-----------+------+---------------------+---------+------+--------+|  7839 | KING  | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 | NULL |     10 ||  7902 | FORD  | ANALYST   | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL |     20 ||  7788 | SCOTT | ANALYST   | 7566 | 1982-12-09 00:00:00 | 3000.00 | NULL |     20 |+-------+-------+-----------+------+---------------------+---------+------+--------+3 rows in set (.00 sec)总结：limit限定显示前多少行，可与order by联合使用

4.聚合函数

count() sum()函数用法：#1.各个部门的薪水和mysql> select deptno,sum(sal) from  emp group by deptno;+--------+----------+| deptno | sum(sal) |+--------+----------+|     10 |  8750.00 ||     20 | 10875.00 ||     30 |  9400.00 |+--------+----------+3 rows in set (.01 sec)
#2.group by字段必须出现在select字段后面   各个部门的各个岗位的薪水和mysql> select deptno,job, sum(sal) from  emp group by deptno ,job;+--------+-----------+----------+| deptno | job       | sum(sal) |+--------+-----------+----------+|     10 | CLERK     |  1300.00 ||     10 | MANAGER   |  2450.00 ||     10 | PRESIDENT |  5000.00 ||     20 | ANALYST   |  6000.00 ||     20 | CLERK     |  1900.00 ||     20 | MANAGER   |  2975.00 ||     30 | CLERK     |   950.00 ||     30 | MANAGER   |  2850.00 ||     30 | SALESMAN  |  5600.00 |+--------+-----------+----------+9 rows in set (.01 sec)
#3.having    薪水和>5000的各个部门的各个岗位mysql> select deptno,job,  sum(sal)     -> from  emp     -> group by deptno ,job    -> having  sum(sal)>5000; +--------+----------+----------+| deptno | job      | sum(sal) |+--------+----------+----------+|     20 | ANALYST  |  6000.00 ||     30 | SALESMAN |  5600.00 |+--------+----------+----------+2 rows in set (.00 sec)#4.常用组合where  order  limit select deptno,job,  sum(sal) as sum_salfrom  emp where job='SALESMAN'group by deptno ,jobhaving  sum(sal)>5000 order by sum(sal) desc limit 1;

下面介绍下join及union的用法
数据准备：

create table testa(aid int,aname varchar(40));
create table testb(bid int,bname varchar(40),age int);
insert into testa values(1,'xiaoming');insert into testa values(2,'LY');insert into testa values(3,'KUN');insert into testa values(4,'ZIDONG');insert into testa values(5,'HB');

insert into testb values(1,'xiaoming',10);insert into testb values(2,'LY',100);insert into testb values(3,'KUN',200);insert into testb values(4,'ZIDONG',110);insert into testb values(6,'niu',120);insert into testb values(7,'meng',130);insert into testb values(8,'mi',170);

5.left join

mysql> select    -> a.aid,a.aname,    -> b.bid,b.bname,b.age    -> from testa as a    -> left join testb as b on a.aid=b.bid; +------+----------+------+----------+------+| aid  | aname    | bid  | bname    | age  |+------+----------+------+----------+------+|    1 | xiaoming |    1 | xiaoming |   10 ||    2 | LY       |    2 | LY       |  100 ||    3 | KUN      |    3 | KUN      |  200 ||    4 | ZIDONG   |    4 | ZIDONG   |  110 ||    5 | HB       | NULL | NULL     | NULL |+------+----------+------+----------+------+5 rows in set (.00 sec)总结：a left join b  a表全，用b表去匹配a表LEFT JOIN 关键字会从左表 (a) 那里返回所有的行，即使在右表 (b) 中没有匹配的行,匹配不到的列用NULL代替

6.right join

mysql> select    -> a.aid,a.aname,    -> b.bid,b.bname,b.age    -> from testa as a    -> right join testb as b on a.aid=b.bid;+------+----------+------+----------+------+| aid  | aname    | bid  | bname    | age  |+------+----------+------+----------+------+|    1 | xiaoming |    1 | xiaoming |   10 ||    2 | LY       |    2 | LY       |  100 ||    3 | KUN      |    3 | KUN      |  200 ||    4 | ZIDONG   |    4 | ZIDONG   |  110 || NULL | NULL     |    6 | niu      |  120 || NULL | NULL     |    7 | meng     |  130 || NULL | NULL     |    8 | mi       |  170 |+------+----------+------+----------+------+7 rows in set (.00 sec)总结：a right join b  b表全，用a表去匹配b表RIGHT JOIN 关键字会右表 (b) 那里返回所有的行，即使在左表 (a) 中没有匹配的行,匹配不到的列用NULL代替

7.inner join

mysql> select    -> a.aid,a.aname,    -> b.bid,b.bname,b.age    -> from testa as a    -> inner join testb as b on a.aid=b.bid; +------+----------+------+----------+------+| aid  | aname    | bid  | bname    | age  |+------+----------+------+----------+------+|    1 | xiaoming |    1 | xiaoming |   10 ||    2 | LY       |    2 | LY       |  100 ||    3 | KUN      |    3 | KUN      |  200 ||    4 | ZIDONG   |    4 | ZIDONG   |  110 |+------+----------+------+----------+------+4 rows in set (.00 sec)
mysql> select    -> a.aid,a.aname,    -> b.bid,b.bname,b.age    -> from testa as a    -> join testb as b on a.aid=b.bid; +------+----------+------+----------+------+| aid  | aname    | bid  | bname    | age  |+------+----------+------+----------+------+|    1 | xiaoming |    1 | xiaoming |   10 ||    2 | LY       |    2 | LY       |  100 ||    3 | KUN      |    3 | KUN      |  200 ||    4 | ZIDONG   |    4 | ZIDONG   |  110 |+------+----------+------+----------+------+4 rows in set (.00 sec)总结：inner join 与join 效果一样在表中存在至少一个匹配时，INNER JOIN 关键字返回行

8.union与union all

mysql> select aid,aname from testa    -> union    -> select bid,bname from testb;+------+----------+| aid  | aname    |+------+----------+|    1 | xiaoming ||    2 | LY       ||    3 | KUN      ||    4 | ZIDONG   ||    5 | HB       ||    6 | niu      ||    7 | meng     ||    8 | mi       |+------+----------+8 rows in set (0.01 sec)
mysql> select aid,aname from testa    -> union all    -> select bid,bname from testb;+------+----------+| aid  | aname    |+------+----------+|    1 | xiaoming ||    2 | LY       ||    3 | KUN      ||    4 | ZIDONG   ||    5 | HB       ||    1 | xiaoming ||    2 | LY       ||    3 | KUN      ||    4 | ZIDONG   ||    6 | niu      ||    7 | meng     ||    8 | mi       |+------+----------+12 rows in set (.00 sec)总结：union 会去重 union all不去重

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原文链接：https://mp.weixin.qq.com/s/LfGht1XRiwH7sF6492xbOw

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