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A common table expression, or CTE, (in SQL) is a temporary named result set, derived from a simple query and defined within the execution scope of a SELECT, INSERT, UPDATE, or DELETE statement. CTEs can be thought of as alternatives to derived tables ( subquery ), views , and inline user-defined functions.
Common table expressions and recursive queries [ edit ] SQL:1999 added a WITH [RECURSIVE] construct allowing recursive queries, like transitive closure , to be specified in the query language itself; see common table expressions .
Since 1999 the SQL standard allows WITH clauses for subqueries, i.e. named subqueries, usually called common table expressions (also called subquery factoring). CTEs can also be recursive by referring to themselves; the resulting mechanism allows tree or graph traversals (when represented as relations), and more generally fixpoint computations.
This page was last edited on 7 November 2012, at 09:24 (UTC).; Text is available under the Creative Commons Attribution-ShareAlike 4.0 License; additional terms may apply.
In XML, operations such as determining whether one element contains another are extremely common, and the recursive join is perhaps the most obvious way to implement them when the XML data is stored in a relational database. The standard way to define recursive joins in the SQL:1999 standard is by way of recursive common table expressions.
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SELECT list is the list of columns or SQL expressions to be returned by the query. This is approximately the relational algebra projection operation. AS optionally provides an alias for each column or expression in the SELECT list. This is the relational algebra rename operation. FROM specifies from which table to get the data. [3]
Common table expression, a temporary named result set derived from a simple query in SQL; Conditional tail expectation, a valuation of risk management and insurance liability; Chunked transfer encoding, a streaming data transfer mechanism in HTTP