Common Table Expression In SQL Server

Introduction

 

While working with database data, there might appear need to operate over a set of data that does not inherently exist within the system.

 

What Is CTE (Common Table Expression)

 

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. (Source: MSDN).

 

Syntax

With expression_name (columnname1, columnname2)
(
Cte query defination
)

Select columnname from expression_name

Advantages of CTE

• Can be used to create a recursive query.
• Can be substituted for a view.
• Allow grouping by a column which might be derived from a scalar subset.
• Can reference itself multiple times.

Disadvantages of CTE

• CTE’s members cannot use the following clauses of keywords Distinct, Group By, Having, Top, Joins limiting by this type of the queries that can be created and reducing their complexity.
• The Recursive member can refer to the CTE only once.
• Table Variables and CTE’s cannot be passed as parameters in stored procedures.

Create CTE in SQL Server

1. Create Table
   
   
   
   
2. Insert Table Value.
   
   
   
   
3. CTE example,