SQL: avg() function 在 where 子句中

Question

I want the salary of all employees whose sal (salary) is greater than the average salary of all employees, however I get the error "invalid use of group function". How can I use avg() function in where clause?

select   sal 
from emp
where sal> (avg(sal)) ;

Answer 1

You can't use AVG in WHERE clause like that. Try this query:

SELECT sal FROM emp WHERE sal > (SELECT AVG(sal) FROM emp)

Answer 2

you may need to use subquery:

select   sal 
from emp
where sal> (select avg(sal) avgsal from emp) ;

Answer 3

You can use avg as a window function , this normally yields better performance over a sub-query:

select Sal from (
    select Sal, Avg(Sal) over() avgSal
    from Employees
)e
where Sal > avgSal