HAVING

Filter groups after aggregation — the clause for conditions WHERE can't express.

WHERE filters rows, HAVING filters groups

WHERE runs before GROUP BY — it can't see aggregates.
HAVING runs after GROUP BY — it filters the grouped rows, and it can use aggregates.

SELECT customer_id, SUM(amount) AS total
FROM orders
GROUP BY customer_id
HAVING SUM(amount) > 300;

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Use both — filter early, then filter groups

WHERE shrinks the input before grouping (cheaper); HAVING filters the aggregated result.

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Putting status = 'paid' in HAVING would work here only because there's no aggregate on it — but it would scan and group rows you could have dropped first. Row-level conditions belong in WHERE.

Gotchas

HAVING without GROUP BY treats the whole result as one group: SELECT SUM(amount) FROM orders HAVING SUM(amount) > 1000 returns one row or none.
Select-list aliases usually aren't visible in HAVING (same as WHERE) — repeat the expression: HAVING SUM(amount) > 300, not HAVING total > 300. Postgres and SQLite allow the alias; SQL Server and Oracle don't.
Non-aggregated columns in HAVING must be in GROUP BY, just like the select list.

GROUP BY — sets the groups HAVING filters.
WHERE — the row-level filter that runs first.
Pivot without PIVOT — conditional aggregation, often paired with HAVING.

WHERE filters rows, HAVING filters groups

Use both — filter early, then filter groups

Gotchas

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