Lecture 4 - Having

Question 1

What is having?

Answer 1

condition to select/reject a group after grouping!

Question 2

EXAMPLE OF HAVING :

Show the number of employees per project only from those projects
with more than 2 employees. Include the project name in the results.

Answer 2

SELECT P.PNAME, COUNT ()
FROM PROJECT AS P, WORKS_ON AS W
WHERE P.PNUMBER = W.PNO
GROUP BY P.PNAME
HAVING COUNT() > 2

Question 3

What is wrong with this query?

SELECT DNO, COUNT ()
FROM EMPLOYEE
WHERE Salary > 40000
GROUP BY DNO
HAVING COUNT () > 5;

Answer 3

We are filtering out employees with small salary before grouping, we still need to include them in the count however.

Question 4

Can sets in sql be named?

Answer 4

Yes and hence used as a variable