9.2基础查询

9.2.1查询所有的列

*表示所有列

##查询所有的员工信息

Select * from emp;

9.2.2查询指定列

输入特指表里的单独列名进行查询

Select empno,ename,depton from emp;

9.3条件查询where

9.3.1常见的运算符

关系运算符：=、!=、<>、>=、<=

区间：between A and B -》[A,B]

And:并且，和

Or：或者

Not：否，非

Is Not null：非空

In：在什么里面

9.3.2查询年龄为65的女学生（where，and）

Select * from stu where age="65" and gender="female";

+--------+-------+------+--------+

| sid    | sname | age  | gender |

+--------+-------+------+--------+

| S_1004 | liSi  |   65 | female |

+--------+-------+------+--------+

9.3.3查询学号为S_1001或名字为lisi的记录（where，or）

Select * from stu where sid="S_1001"or sname="lisi";

+--------+-------+------+--------+

| sid    | sname | age  | gender |

+--------+-------+------+--------+

| S_1001 | liuYi |   35 | male   |

| S_1004 | liSi  |   65 | female |

+--------+-------+------+--------+

9.3.4查询学号是S_1001，S_1002，S_1003的记录（where，in）

写法一：select * from stu where sid = "S_1001" or sid = "S_1002" or sid = "S_1003";

写法二：select * from stu where sid in("S_1001","S_1002","S_1003");

+--------+----------+------+--------+

| sid    | sname    | age  | gender |

+--------+----------+------+--------+

| S_1001 | liuYi    |   35 | male   |

| S_1002 | chenEr   |   15 | female |

| S_1003 | zhangSan |   95 | male   |

+--------+----------+------+--------+

9.3.5查询学号不是S_1001，S_1002，S_1003的记录（where，not，in）

select * from stu where sid not in("S_1001","S_1002","S_1003");

9.3.6查询年龄为null的记录（where）

Select * from stu weher age is null;

9.3.7查询年龄在20-40之间的记录（between）

方式一：Select * from stu where age >=20 and <=40;

方式二：Select * from stu where age between 20 and 40;

9.3.8查询性别为非男的记录（where，not）

方式一：Select * from stu where gender !=’male’

方式二：Select * from stu where not gender =’male’

方式三：Select * from stu where gender <> ’male’

9.3.9查询名字不为空的学生信息（is not null）

Select * from stu where sname is not null;