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
