表内容操作

就是对表进行

增删改查

insert into user(username,password,email) values('alex','999','sb@oldboy.com')

插入可以一下子插入两行的

delete ffrom user where id=4

update user set username='xxoo' where nid>2

select * from user

select nid from where

注意还有其他的限制条件

比如：

in

not in

between .. and...

 

 select * from user nid in(select nid from tb2 )

where username like 'alex%'

%:代表n个字符。

—：代表一个字符。

LIMIT：从4开始，后边取3个。

select * from user order by nid desc;

select * from user order by password asc,nid desc

select department,count(department) from user group by department;

select max(nid),min(nid),sum(nid),avg(nid)

如果想要对groupby的结果做操作的话，就对groupby 加having

通过union关键字，对两个表进行结合，注意个数一定要一样，union默认会去重，如果不想去重，加个all也可以