A subquery is a query nested in another query.
| Title | Description |
|---|---|
| Scalar Subqueries | Subquery returning a single value |
| Row Subqueries | Subquery returning a row |
| Subqueries and ALL | Return true if the comparison returns true for each row, or the subquery returns no rows. |
| Subqueries and ANY | Return true if the comparison returns true for at least one row returned by the subquery. |
| Subqueries and EXISTS | Returns true if the subquery returns any rows. |
| Subqueries in a FROM Clause | Subqueries are more commonly placed in a WHERE clause, but can also form part of the FROM clause |
| Subquery Optimizations | Articles about subquery optimizations in MariaDB. |
| Subqueries and JOINs | Rewriting subqueries as JOINs, and using subqueries instead of JOINs |
| Subquery Limitations | There are a number of limitations regarding subqueries. |
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https://mariadb.com/kb/en/subqueries/