一、常用聚合函数
求最大值:select max(sal) from emp ;
求最小值:select min(sal) from emp ;
求平均值:select avg(sal) from emp ;
Sum 求和:select sum(sal) from emp ;
Count 统计记录数:select count(ename) from emp ;
(Having 过滤分组:select job,count(ename) as num from EMP t group by job having count(ename)>=2;)
二、空值处理
select ename,nvl(sal,0) sal from emp;
三、分页处理
rownum行号
select e.*,rownum from emp e;
select a.*,rownum rn from (select * from emp) a where rownum<=2;
//获取行号小于等于2的数据
select * from (select a.*,rownum rn from (select * from emp) a where rownum<=3) where rn>1;
//获取行号为2~3的数据
四、oracle中的运算
select 2+1 from dual;
select 2-1 from dual;
select 2*1 from dual;
select 2/1 from dual;
五、条件判断
Between and 范围查询:
select * from emp where sal between 900 and 1500;
select * from emp where sal>=900 and sal<=1500;
六、In 集合范围:
select ename,hiredate from emp where ename in (select distinct ename from bonus)
七、Like 模糊查询:
select * from emp where ename like '%M%
select * from emp where ename like 'M%'
select * from emp where ename like '_M%'