The number of columns returned from the anchor member must be the same number of columns returned from the recursive member. Additionally the anchor member queries need to appear in the CTE prior to the recursive member queries.
An anchor member query definition will not reference the CTE whereas the recursive member will reference the CTE. One query definition is known as the anchor member and the other query definition is known as the recursive member. A recursive CTE contains at least two query definitions, which are SELECT statements. When this is done it is called a recursive CTE. The final result set from a recursive CTE in SQL Server is the joined set of all the result sets from all the calls of the recursive query.Ī CTE can reference itself. The recursive process keeps calling itself until a condition is found that indicates it should not call itself anymore. Each iteration of the recursive process returns a subset of the answer. This may sound confusing, but we'll see some examples shortly.īelow are some clauses that can't be used in a CTE:Ī recursive process is a process that calls itself. When you define multiple CTE's, a CTE that references another CTE needs to be define after the CTE it is referencing. If the CTE is part of a batch then the statement prior to the WITH clause must end with a semi-colon. "CTE Definition" is a SELECT that defines the result set of the CTE.Ī CTE definition needs to be followed by a single INSERT, UPDATE, DELETE, or SELECT statement that references the CTE."Column 1, Column2,…" are the names of the columns returned from the CTE (only required if column names are not provided, or are not unique).WITH (Column1, Column2, …) AS (CTE Definition) By using a CTE you can write and name a TSQL SELECT statement and then reference the named statement later on much like you would reference a table or a view. With the introduction of CTE's by Microsoft you now have a different way to build and document complex pieces of TSQL code.
#Sql server cte how to
In this article I be exploring how to define and use CTE's. A CTE is a temporary result set defined by a simple query, and is used within the execution scope of a single INSERT, UPDATE, DELETE, or SELECT statement.
With the rollout of SQL Server 2005, Microsoft introduced a new query construct called a common table expression (CTE).