Although you usually use subqueries as search conditions in the WHERE clause, sometimes you can also use them in the HAVING clause of a query. When a subquery appears in the HAVING clause, like any expression in the HAVING clause, it is used as part of the row group selection.
Here is a request that lends itself naturally to a query with a subquery in the HAVING clause: "Which products' average in-stock quantity is more than double the average number of each item ordered per customer?"
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