mysql查询语句

Posted 2020-10-27

select 字段1，字段2 from 表1，表2 where 字段 group by 分组字段 having 字段 order by 字段  ASC|DESC  limit m,n 

一、查询所有

select * from student;

select name as 姓名 from student;

select name 姓名 from student;

二、条件查询

1.查询学生id等于1

selet * from student where student_id;

2.查询name字段为null

selet * from student where name is null;

3.查询name字段不为null

select * from student where name is not null;

4.查询name字段为空字符串

select * from student where name =‘‘;

5.查询name字段不为空字符串且不为null

select * from student where name !=‘‘;

6.查询city字段存在河南省和山东省的数据

select * from where city in(‘山东省‘,‘河南省‘);

7.查询age在25到30之间

select * from student where age between 25 and 30;

8.查询age不在20到30之间

select * from student where age not between 20 and 30;

9.查询第一个字是郭的数据

select * from student where name like ‘郭%‘;

10查询第一个字是郭的两个字得数据

select * from student where name like ‘郭_‘;

11查询存在郭的字得数据

select * from student where name like ‘%郭%‘;

三、分组查询

1.分组性别

select sex,count(*) from student group by sex;

2.分组性别前条件查询

select sex,count(*) from student where name !=‘李白‘ group by sex;

3.分组性别后条件查询

select sex,count(*) from student group by sex having count(*)>5;

4.查询后分组然后再条件查询

select sex,count(*) from student where name !=‘李白‘ group by sex having count(*)>5;

四、排序查询

 1.降序排序

select * from student order by salary desc;

2.降序后再升序排序

 select * from student order by salary desc,bonus asc;

五、聚合函数

count(*)
sum(salary)
avg(salary)
min(salary)
max(salary)