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;

posted @ 2021-04-20 18:32  晚风踩着云  阅读(31)  评论(0编辑  收藏  举报