Is there a way to make this SQL more efficient?

Question

Consider the following tables:

department

deptid      (type:INT)
deptname    (type: TEXT)
hours       (type:INT)
active      (type:BIT)


        

Answer 1

This is shorter and probably performs faster too

SELECT e1.empname, d.deptname
from (
      SELECT e2.deptid
      FROM employee AS e2
      GROUP BY e2.deptid
      HAVING COUNT(e2.empid) >= 4
    ) G
inner join employee AS e1 on e1.deptid = G.deptid
INNER JOIN department AS d on d.deptid = G.deptid
ORDER BY e1.empname;

Start with the grouping. You don't need COUNT from the inner query. Then, join to both tables just to get the names.

INNER JOIN is used because once the count is complete, we already know that

1. the employees exist
2. the department exists

Answer 2

Try this query, it will work properly.

select empname,deptname from employee,department
where 
employee.deptid=department.deptid and employee.deptid
in
(
  select deptId from employee group by deptid having count(*)>=4
) 
order by empname