MySQL条件查询
操作的表
mysql> select * from emp;
| EMPNO | ENAME | JOB | MGR | HIREDATE | SAL | COMM | DEPTNO |
|---|---|---|---|---|---|---|---|
| 7369 | SMITH | CLERK | 7902 | 1980-12-17 | 800.00 | NULL | 20 |
| 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600.00 | 300.00 | 30 |
| 7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 | 30 |
| 7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975.00 | NULL | 20 |
| 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 | 30 |
| 7698 | BLAKE | MANAGER | 7839 | 1981-05-01 | 2850.00 | NULL | 30 |
| 7782 | CLARK | MANAGER | 7839 | 1981-06-09 | 2450.00 | NULL | 10 |
| 7788 | SCOTT | ANALYST | 7566 | 1987-04-19 | 3000.00 | NULL | 20 |
| 7839 | KING | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL | 10 |
| 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 | 0.00 | 30 |
| 7876 | ADAMS | CLERK | 7788 | 1987-05-23 | 1100.00 | NULL | 20 |
| 7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950.00 | NULL | 30 |
| 7902 | FORD | ANALYST | 7566 | 1981-12-03 | 3000.00 | NULL | 20 |
| 7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300.00 | NULL | 10 |
其每个字段的字段名分别为员工编号、员工姓名、员工职位、员工上级领导编号、员工雇佣日期，员工薪水、员工津贴、员工部门编号。
1.条件查询概述
语法格式：
select
字段,字段…
from
表名
where
条件;
执行顺序：先from，然后where，最后select
查询工资等于5000的员工姓名？
select ename,sal from emp where sal=5000;
+-------+---------+
| ename | sal |
+-------+---------+
| KING | 5000.00 |
+-------+---------+
查询SMITH的工资？
select sal from emp where ename = ‘SMITH’; // 字符串使用单引号括起来。
+--------+
| sal |
+--------+
| 800.00 |
+--------+
找出工资高于3000的员工？
select ename,sal from emp where sal > 3000;
+-------+---------+
| ename | sal |
+-------+---------+
| KING | 5000.00 |
+-------+---------+
select ename,sal from emp where sal >= 3000;
select ename,sal from emp where sal < 3000;
select ename,sal from emp where sal <= 3000;
找出工资不等于3000的？
select ename,sal from emp where sal!=3000;
select ename,sal from emp where sal <> 3000;
+--------+---------+
| ename | sal |
+--------+---------+
| SMITH | 800.00 |
| ALLEN | 1600.00 |
| WARD | 1250.00 |
| JONES | 2975.00 |
| MARTIN | 1250.00 |
| BLAKE | 2850.00 |
| CLARK | 2450.00 |
| KING | 5000.00 |
| TURNER | 1500.00 |
| ADAMS | 1100.00 |
| JAMES | 950.00 |
| MILLER | 1300.00 |
+--------+---------+
找出工资在1100和3000之间的员工，包括1100和3000？
select ename,sal from emp where sal <= 3000 and sal>=1100;
select ename,sal from emp where sal between 1100 and 3000; // between…and…是闭区间 [1100 ~ 3000]
select ename,sal from emp where sal between 3000 and 1100; // 查询不到任何数据
between and在使用的时候必须左小右大。
2.条件查询between and]
操作的表的各个字段，具体值见第一节
| EMPNO | ENAME | JOB | MGR | HIREDATE | SAL | COMM | DEPTNO |
|---|
其每个字段的字段名分别为员工编号、员工姓名、员工职位、员工上级领导编号、员工雇佣日期，员工薪水、员工津贴、员工部门编号。
between and在使用的时候必须左小右大。
between and除了可以使用在数字方面之外，还可以使用在字符串方面。
select ename from emp where ename between ‘A’ and ‘D’;
+-------+
| ename |
+-------+
| ALLEN |
| BLAKE |
| CLARK |
| ADAMS |
+-------+
select ename from emp where ename between ‘A’ and ‘D’; // 左闭右开。
3.条件查询is null和is not null
| EMPNO | ENAME | JOB | MGR | HIREDATE | SAL | COMM | DEPTNO |
|---|
其每个字段的字段名分别为员工编号、员工姓名、员工职位、员工上级领导编号、员工雇佣日期，员工薪水、员工津贴、员工部门编号。
找出哪些人津贴为NULL？
在数据库当中NULL不是一个值，代表什么也没有，为空。
空不是一个值，不能用等号衡量。
必须使用 is null或者is not null
select ename,sal,comm from emp where comm is null;
+--------+---------+------+
| ename | sal | comm |
+--------+---------+------+
| SMITH | 800.00 | NULL |
| JONES | 2975.00 | NULL |
| BLAKE | 2850.00 | NULL |
| CLARK | 2450.00 | NULL |
| SCOTT | 3000.00 | NULL |
| KING | 5000.00 | NULL |
| ADAMS | 1100.00 | NULL |
| JAMES | 950.00 | NULL |
| FORD | 3000.00 | NULL |
| MILLER | 1300.00 | NULL |
+--------+---------+------+
select ename,sal,comm from emp where comm = null;是错误的
Empty set (0.00 sec)
找出哪些人津贴不为NULL？
select ename,sal,comm from emp where comm is not null;
+--------+---------+---------+
| ename | sal | comm |
+--------+---------+---------+
| ALLEN | 1600.00 | 300.00 |
| WARD | 1250.00 | 500.00 |
| MARTIN | 1250.00 | 1400.00 |
| TURNER | 1500.00 | 0.00 |
+--------+---------+---------+
0表示数字0，而不是为空
找出哪些人没有津贴？
select ename,sal,comm from emp where comm is null or comm = 0;
+--------+---------+------+
| ename | sal | comm |
+--------+---------+------+
| SMITH | 800.00 | NULL |
| JONES | 2975.00 | NULL |
| BLAKE | 2850.00 | NULL |
| CLARK | 2450.00 | NULL |
| SCOTT | 3000.00 | NULL |
| KING | 5000.00 | NULL |
| TURNER | 1500.00 | 0.00 |
| ADAMS | 1100.00 | NULL |
| JAMES | 950.00 | NULL |
| FORD | 3000.00 | NULL |
| MILLER | 1300.00 | NULL |
+--------+---------+------+
and是并且，or是或者，两者都要选
4.and和or的优先级的问题
| EMPNO | ENAME | JOB | MGR | HIREDATE | SAL | COMM | DEPTNO |
|---|
其每个字段的字段名分别为员工编号、员工姓名、员工职位、员工上级领导编号、员工雇佣日期，员工薪水、员工津贴、员工部门编号。
找出工作岗位是MANAGER和SALESMAN的员工？
select ename,job from emp where job = ‘MANAGER’ or job = ‘SALESMAN’;
注意，这里肯定是用or，不可能有一个人既是经理又是销售员
and被翻译成并且，or是或者
+--------+----------+
| ename | job |
+--------+----------+
| ALLEN | SALESMAN |
| WARD | SALESMAN |
| JONES | MANAGER |
| MARTIN | SALESMAN |
| BLAKE | MANAGER |
| CLARK | MANAGER |
| TURNER | SALESMAN |
+--------+----------+
and和or联合起来用：找出薪资大于1000的并且部门编号是20或30部门的员工。
select ename,sal,deptno from emp where sal>1000 and deptno=‘20’ or deptno='30’
错误的
但是查询结果里面竟然出来了一个950
+--------+---------+--------+
| ename | sal | deptno |
+--------+---------+--------+
| ALLEN | 1600.00 | 30 |
| WARD | 1250.00 | 30 |
| JONES | 2975.00 | 20 |
| MARTIN | 1250.00 | 30 |
| BLAKE | 2850.00 | 30 |
| SCOTT | 3000.00 | 20 |
| TURNER | 1500.00 | 30 |
| ADAMS | 1100.00 | 20 |
| JAMES | 950.00 | 30 |
| FORD | 3000.00 | 20 |
+--------+---------+--------+
为什么950先出来，因为and和or组队后，优先级最高的是and, sal>1000 and deptno='20’这两个写在一块，会先查满足这两个条件的，然后再查单独满足deptno='30’的员工，也就是部门号为30的都会查询出来。
select ename,sal,deptno from emp where sal>1000 and (deptno=‘20’ or deptno=‘30’)（正确的）
+--------+---------+--------+
| ename | sal | deptno |
+--------+---------+--------+
| ALLEN | 1600.00 | 30 |
| WARD | 1250.00 | 30 |
| JONES | 2975.00 | 20 |
| MARTIN | 1250.00 | 30 |
| BLAKE | 2850.00 | 30 |
| SCOTT | 3000.00 | 20 |
| TURNER | 1500.00 | 30 |
| ADAMS | 1100.00 | 20 |
| FORD | 3000.00 | 20 |
+--------+---------+--------+
注意：当运算符的优先级不确定的时候加小括号。
5.条件查询in
| EMPNO | ENAME | JOB | MGR | HIREDATE | SAL | COMM | DEPTNO |
|---|
其每个字段的字段名分别为员工编号、员工姓名、员工职位、员工上级领导编号、员工雇佣日期，员工薪水、员工津贴、员工部门编号。
in等同于or：找出工作岗位是MANAGER和SALESMAN的员工？
select ename,job from emp where job = ‘SALESMAN’ or job = ‘MANAGER’;
select ename,job from emp where job in(‘SALESMAN’, ‘MANAGER’);
+--------+----------+
| ename | job |
+--------+----------+
| ALLEN | SALESMAN |
| WARD | SALESMAN |
| JONES | MANAGER |
| MARTIN | SALESMAN |
| BLAKE | MANAGER |
| CLARK | MANAGER |
| TURNER | SALESMAN |
+--------+----------+
select ename,job from emp where sal in(800, 5000); // in后面的值不是区间，是具体的值。找出工资800和5000的
+-------+-----------+
| ename | job |
+-------+-----------+
| SMITH | CLERK |
| KING | PRESIDENT |
+-------+-----------+
not in: 不在这几个值当中。
select ename,job from emp where sal not in(800, 5000);
6.模糊查询like
| EMPNO | ENAME | JOB | MGR | HIREDATE | SAL | COMM | DEPTNO |
|---|
其每个字段的字段名分别为员工编号、员工姓名、员工职位、员工上级领导编号、员工雇佣日期，员工薪水、员工津贴、员工部门编号。
找出名字当中含有O的？
（在模糊查询当中，必须掌握两个特殊的符号，一个是%，一个是_）
%代表任意多个字符，_代表任意1个字符。
select ename from emp where ename like ‘%O%’;
+-------+
| ename |
+-------+
| JONES |
| SCOTT |
| FORD |
+-------+
找出第二个字母是A的
select ename from emp where ename like ‘_A%’
+--------+
| ename |
+--------+
| WARD |
| MARTIN |
| JAMES |
+--------+
找出名字中有下划线的？
mysql> select * from t_user;
| id | name |
+------+----------+
| 1 | zhangsan |
| 2 | lisi |
| 3 | WANG_WU |
+------+----------+
select name from t_user where name like ‘%_%’;
| name |
+----------+
| zhangsan |
| lisi |
| WANG_WU |
+----------+
这里的_下划线拥有特殊的含义，只表示一个字符。我们想让它成为一个普通的下划线字符，而不具有特殊含义，我们可以使用转义字符
select name from t_user where name like ‘%_%’;
| name |
+---------+
| WANG_WU |
+---------+
找出名字中最后一个字母是T的？
select ename from emp where ename like '%T’
+-------+
| ename |
+-------+
| SCOTT |
+-------+
注：本版块中MySQL所用到的数据库bjpowernode代码如下，可以直接运行生成数据库文件
DROP TABLE IF EXISTS EMP;
DROP TABLE IF EXISTS DEPT;
DROP TABLE IF EXISTS SALGRADE;
CREATE TABLE DEPT
(DEPTNO int(2) not null ,
DNAME VARCHAR(14) ,
LOC VARCHAR(13),
primary key (DEPTNO)
);
CREATE TABLE EMP
(EMPNO int(4) not null ,
ENAME VARCHAR(10),
JOB VARCHAR(9),
MGR INT(4),
HIREDATE DATE DEFAULT NULL,
SAL DOUBLE(7,2),
COMM DOUBLE(7,2),
primary key (EMPNO),
DEPTNO INT(2)
)
;
CREATE TABLE SALGRADE
( GRADE INT,
LOSAL INT,
HISAL INT );
INSERT INTO DEPT ( DEPTNO, DNAME, LOC ) VALUES (
10, 'ACCOUNTING', 'NEW YORK');
INSERT INTO DEPT ( DEPTNO, DNAME, LOC ) VALUES (
20, 'RESEARCH', 'DALLAS');
INSERT INTO DEPT ( DEPTNO, DNAME, LOC ) VALUES (
30, 'SALES', 'CHICAGO');
INSERT INTO DEPT ( DEPTNO, DNAME, LOC ) VALUES (
40, 'OPERATIONS', 'BOSTON');
commit;
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7369, 'SMITH', 'CLERK', 7902, '1980-12-17'
, 800, NULL, 20);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7499, 'ALLEN', 'SALESMAN', 7698, '1981-02-20'
, 1600, 300, 30);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7521, 'WARD', 'SALESMAN', 7698, '1981-02-22'
, 1250, 500, 30);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7566, 'JONES', 'MANAGER', 7839, '1981-04-02'
, 2975, NULL, 20);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7654, 'MARTIN', 'SALESMAN', 7698, '1981-09-28'
, 1250, 1400, 30);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7698, 'BLAKE', 'MANAGER', 7839, '1981-05-01'
, 2850, NULL, 30);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7782, 'CLARK', 'MANAGER', 7839, '1981-06-09'
, 2450, NULL, 10);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7788, 'SCOTT', 'ANALYST', 7566, '1987-04-19'
, 3000, NULL, 20);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7839, 'KING', 'PRESIDENT', NULL, '1981-11-17'
, 5000, NULL, 10);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7844, 'TURNER', 'SALESMAN', 7698, '1981-09-08'
, 1500, 0, 30);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7876, 'ADAMS', 'CLERK', 7788, '1987-05-23'
, 1100, NULL, 20);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7900, 'JAMES', 'CLERK', 7698, '1981-12-03'
, 950, NULL, 30);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7902, 'FORD', 'ANALYST', 7566, '1981-12-03'
, 3000, NULL, 20);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7934, 'MILLER', 'CLERK', 7782, '1982-01-23'
, 1300, NULL, 10);
commit;
INSERT INTO SALGRADE ( GRADE, LOSAL, HISAL ) VALUES (
1, 700, 1200);
INSERT INTO SALGRADE ( GRADE, LOSAL, HISAL ) VALUES (
2, 1201, 1400);
INSERT INTO SALGRADE ( GRADE, LOSAL, HISAL ) VALUES (
3, 1401, 2000);
INSERT INTO SALGRADE ( GRADE, LOSAL, HISAL ) VALUES (
4, 2001, 3000);
INSERT INTO SALGRADE ( GRADE, LOSAL, HISAL ) VALUES (
5, 3001, 9999);
commit;