Why we use CTE in sql server?

SAM ROCK

11y2.6k

Any body can suggest me what is the best use of CTE in sql server.

6 Replies

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geetha geetha4y ago
Reason for Using common Table expression for simplify the complex joins and Subqueries.

CTE is a Temporary result set, it can be referenced with select, insert, update, delete statement. CTE used in a view also. CTE results are not stored anywhere, they don’t produce a result. We use CTE for recursive query. CTE provides some advantages like improving readability and easily maintaining the complex queries.

Query for create a CTE expression:

with CTE_emp(empid,empname,address)

AS

(

Select empid,empname,address from emp

)

select * from CTE_emp

Alternate Solution: Bigquery is an alternate solution for using recursive CTE.
Sanwar Ranwa8y ago
https://www.essentialsql.com/introduction-common-table-expressions-ctes/
SAM ROCK11y ago
Thanks Bhushan Bhasme
SAM ROCK11y ago
Thanks Francis
Bhushan Bhasme11y ago
Hi Sam,
A common table expression (CTE) can be thought of as a temporary result set that is defined within the execution scope of a single SELECT, INSERT, UPDATE, DELETE, or CREATE VIEW statement. A CTE is similar to a derived table in that it is not stored as an object and lasts only for the duration of the query. Unlike a derived table, a CTE can be self-referencing and can be referenced multiple times in the same query.
A CTE can be used to:
Create a recursive query. For more information, see Recursive Queries Using Common Table Expressions
Substitute for a view when the general use of a view is not required; that is, you do not have to store the definition in metadata.
Enable grouping by a column that is derived from a scalar subselect, or a function that is either not deterministic or has external access.
Reference the resulting table multiple times in the same statement.
Using a CTE offers the advantages of improved readability and ease in maintenance of complex queries. The query can be divided into separate, simple, logical building blocks. These simple blocks can then be used to build more complex, interim CTEs until the final result set is generated.
CTEs can be defined in user-defined routines, such as functions, stored procedures, triggers, or views.
For More Info Please Visit Below Link
https://technet.microsoft.com/en-us/library/ms190766%28v=sql.105%29.aspx
Francis Susaimichael11y ago
CTE can be used in the below scenarios:

1) If you want to store the result of the query that lasts only the duration of the query.
2) If you want to self-reference it in the query.

In the above 2 scenarios, you can use Derived tables also, but it won't give the above flexibility. In that case you can go with CTE.

Hope this helps a bit!