mysql 表相关操作(1)

查询语句

select * from t_dept
select empno,ename,sal from t_emp  

select
   empno,
   sal * 12 as "income"
from t_emp

分页

select empno,ename from t_emp limit 10,5

  去除重复字段

  select job from t_emp      会出现重复的

CLERK
SALESMAN
SALESMAN
MANAGER
SALESMAN
MANAGER
MANAGER
ANALYST
PRESIDENT

select DISTINCT job from t_emp    加上关键字 DISTINCT  就不会出现重复   只能使用一个字段

CLERK
SALESMAN
MANAGER
ANALYST
PRESIDENT

排序  DESC 降序  ASC升序

select empno,ename,sal,deptno from t_emp ORDER BY sal DESC

条件查询 

select empno,ename,sal,deptno from t_emp where deptno in (10,20) and sal >= 2000 order by deptno

select empno,ename,sal,hiredate,deptno
from t_emp
where deptno = 10
AND (sal + IFNULL(comm,0))* 12 > 15000
AND DATEDIFF(NOW(),hiredate)/365 >= 20

select empno,ename,sal,hiredate,deptno
from t_emp
where deptno in (10,20,30) and job != 'SALESMAN'

is null  / is not null

select empno,ename,sal,hiredate,deptno,comm
from t_emp
where comm is null

BETWEEN ... AND ...

select empno,ename,sal,hiredate,deptno,comm
from t_emp
where comm is null
AND sal BETWEEN 2000 AND 3000

LIKE  模糊查询

select empno,ename,sal,hiredate,deptno,comm
from t_emp
where comm is null
AND sal BETWEEN 2000 AND 3000
AND ename LIKE '%A%'