HAVING Clause

HAVING Clause

HAVING filters groups after grouping. This is different from WHERE, which filters rows before grouping.

The problem

You cannot use aggregate functions in WHERE:

-- This FAILS:
SELECT Country, COUNT(*) FROM Customers
WHERE COUNT(*) > 1
GROUP BY Country;

The fix: HAVING

SELECT Country, COUNT(*)
FROM Customers
GROUP BY Country
HAVING COUNT(*) > 1;

Keeps only countries with more than one customer.

WHERE vs HAVING

Both together

SELECT CategoryID, AVG(Price)
FROM Products
WHERE Price > 10          -- filter rows first
GROUP BY CategoryID
HAVING AVG(Price) > 20;   -- then filter groups

Order of clauses

SELECT → FROM → WHERE → GROUP BY → HAVING → ORDER BY

TL;DR

• HAVING filters groups.
• WHERE filters rows.
• WHERE comes before GROUP BY; HAVING comes after.
• Use HAVING with aggregate functions.