HAVING versus WHERE

Filtering groups after aggregation, and why the order matters.

What you'll be able to do

Choose between WHERE and HAVING
Combine both in one query
Explain the performance implication

The distinction

WHERE filters rows before grouping. HAVING filters groups after aggregation.

SELECT region, SUM(total) AS revenue
FROM orders
WHERE order_date >= '2024-01-01'   -- rows first
GROUP BY region
HAVING SUM(total) > 100000;        -- then groups

Which to use

If the condition is on a raw column value, it belongs in WHERE. If it is on an aggregate, it must go in HAVING.

Putting a row-level condition in HAVING usually still works but is slower — more rows reach the grouping step only to be discarded afterwards.

HAVING without GROUP BY

Legal, if unusual. The whole table is treated as one group:

SELECT SUM(total) FROM orders HAVING SUM(total) > 1000000;

Returns the total, or no rows at all if it fails the test.

Aliases in HAVING

Most dialects require you to repeat the aggregate expression rather than referencing the SELECT alias, because HAVING is evaluated before SELECT. MySQL and Postgres are more permissive, but repeating it is portable.

Key points

WHERE filters rows before grouping; HAVING filters groups after
Row-level conditions belong in WHERE — it is cheaper
HAVING is evaluated before SELECT, so aliases may not be available

Check yourself