having

--对分组之后的信息进行过滤
--输出部门平均工资大于2000的部门的部门编号 部门的平均工资
select deptno,avg(sal)
from emp
group by deptno
having avg(sal) >2000

select deptno，avg(sal) as "平均工资"
from emp
group by deptno
having avg(sal) > 2000

select deptno "部门编号",avg(sal) as "平均工资"
from emp
group by deptno
having deptno >1

select deptno,avg(sal) as "平均工资"
from emp
group by deptno

————————————————————————————————————————————————————

HAVING = 分组后的筛选WHERE = 分组前的筛选

SELECT deptno, AVG(sal)
FROM emp
WHERE sal > 1000 -- 1. 先筛选：只看工资>1000的员工
GROUP BY deptno -- 2. 再按部门分组算平均
HAVING AVG(sal) > 2000; -- 3. 最后筛选：只留平均工资>2000的部门