In addition to being able to group data using
GROUP BY, SQL also allows you to filter which groups to include and which to exclude.
For instance, imagine that we want to see how many movies of different genres were produced each year, but we only care about years and genres with at least 10 movies.
We can’t use
WHERE here because we don’t want to filter the rows; we want to filter groups.
This is where
HAVING comes in.
HAVING is very similar to
WHERE. In fact, all types of
WHERE clauses you learned about thus far can be used with
We can use the following for the problem:
SELECT year, genre, COUNT(name) FROM movies GROUP BY 1, 2 HAVING COUNT(name) > 10;
HAVING statement always comes after
GROUP BY, but before
ORDER BY and
Suppose we have the query below:
SELECT price, ROUND(AVG(downloads)), COUNT(*) FROM fake_apps GROUP BY price;
It returns the average downloads (rounded) and the number of apps – at each price point.
However, certain price points don’t have very many apps, so their average downloads are less meaningful.
HAVING clause to restrict the query to price points that have more than 10 apps.