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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, 0, 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 (0.00 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 (0.00 sec)
总结：
% 表示任意 0 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 | 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 (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 (0.00 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 (0.00 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 (0.00 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 (0.01 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 (0.01 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 (0.00 sec)
#4. 常用组合 where order limit
select deptno,job, sum(sal) as sum_sal
from emp
where job=’SALESMAN’
group by deptno ,job
having 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 (0.00 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 (0.00 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 (0.00 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 (0.00 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 (0.00 sec)
总结：
union 会去重 union all 不去重
