A query can use numerous nested derived-table expressions, which are SQL expressions that define a SQL-derived table. In the following example, the innermost derived-table expression defines SQL-derived table dt_1, the select from forming the derived-table expression that defines SQL-derived table dt_2.
select postalcode from (select postalcode from (select postalcode from authors) dt_1) dt_2
The degree of nesting is limited to 25.
