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A subquery can use values from the outer query, in which case it is known as a [[correlated subquery]].
Since 1999 the SQL standard allows named subqueries called [[common table expression]]s (named and designed after the IBM DB2 version 2 implementation; Oracle calls these [[subquery factoring]]). CTEs can also be [[recursive]] by referring to themselves; [[Hierarchical and recursive queries in SQL|the resulting mechanism]] allows tree or graph traversals (when represented as relations), and more generally [[fixpoint]] computations.<ref name="smetric">{{Cite web |title=Subquery or CTE, which one is winner? |author=Loretta F. Gillock |work=smetric.com |access-date=17 July 2020 |url= https://smetric.com/sql-subquery-or-cte-which-one-is-winner/ |language=en-US}}</ref>
=== Derived table ===
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