前言：

本篇文章主要簡(jiǎn)介下MySQL中where,group by ,order by ,limit,join,union ,union all,子表等查詢語(yǔ)法。

測(cè)試數(shù)據(jù)準(zhǔn)備

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.模糊查詢

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)

總結(jié)：%表示任意0個(gè)或多個(gè)字符，可匹配任意類型和長(zhǎng)度的字符；_表示任意單個(gè)字符，匹配單個(gè)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)

總結(jié)：order by排序默認(rèn)按asc升序來(lái)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)

總結(jié)：limit限定顯示前多少行，可與order by聯(lián)合使用

4.聚合函

count() sum()函數(shù)用法：#1.各個(gè)部門的薪水和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字段必須出現(xiàn)在select字段后面 各個(gè)部門的各個(gè)崗位的薪水和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的各個(gè)部門的各個(gè)崗位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.常用組合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;

下面介紹下join及union的用法數(shù)據(jù)準(zhǔn)備：

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)

總結(jié)：a left join b a表全，用b表去匹配a表LEFT JOIN 關(guān)鍵字會(huì)從左表 (a) 那里返回所有的行，即使在右表 (b) 中沒(méi)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)

總結(jié)：a right join b b表全，用a表去匹配b表RIGHT JOIN 關(guān)鍵字會(huì)右表 (b) 那里返回所有的行，即使在左表 (a) 中沒(méi)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)

總結(jié)：inner join 與join 效果一樣在表中存在至少一個(gè)匹配時(shí)，INNER JOIN 關(guān)鍵字返回行

8.union與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)

總結(jié)：union 會(huì)去重 union all不去重

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