In this blog, I will show step by step how to use Common Table Expression or What we called CTE in SQL Query. explain how its works and why we need to do this. Let’s Go.
I. CTE means
A Common Table Expression also called CTE in short form, is a temporary named result set that you can reference within a SELECT, INSERT, UPDATE, or DELETE statement. The CTE can also be used in a View. In this article, we will see in detail how to create and use CTEs from our SQL Server.
II. Are CTE faster than subquery?
Both CTEs and Sub-Query are best but you can use them differently. The only advantage is of CTE over the Sub-Query is you can do two or more CTEs in one statement that subquery can’t. Also, you can define CTE to other CTEs, You need to define first the CTE1 to call it in CTE2. a CTE is more readable than a subquery.
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III. CTE vs View?
Also Know, what is difference between CTE and view? A CTE is in essence a temporary view. It’s a named query that only exists for a single query after its defined. It simplifies writing queries with complex subqueries that are repeatedly used or referenced. A CTE can contain a reference to itself, whereas a view can’t.
For more information and tutorial about View, click the botton below.
IV. Create CTE Query
Let’s do it! I am assuming that you are connected and open your SQL Server Database and facing in SQL query windows.
SAMPLE TABLE1: Candidates
SAMPLE TABLE2: Reports
WITH CTE_Reports as ( Select company, candidate_id, score From reports Where company != 'ITCamp' ), CTE_Candidates as ( Select * From candidates ) Select * From CTE_Candidates A inner Join CTE_Reports B On A.id = B.candidate_id
Actually, we can do it directly to join these two tables but I want to simplify how to use and how to make CTE in a simple way. You can do it and explore about CTEs in your own way of queries.
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