In this chapter, you learned that
A subquery is a query placed within a SELECT , UPDATE , or DELETE statement.
Single row subqueries return zero or one row.
Multiple row subqueries return one or more rows.
Multiple column subqueries return more than one column.
Correlated subqueries reference one or more columns in the outer SQL statement.
Nested subqueries are subqueries placed within another subquery.
In the next chapter, you ll learn about advanced queries.