What is the With Clause in SQL Server | SQL WITH Clause Tricks
Summary: In this article, you will learn What is the With Clause in SQL Server. Let’s understand with an example in detail that How to break down complex SQL queries into smaller ones that make it simple for debugging & processing the most complex queries.
What is the With Clause in SQL Server?
SQL WITH clause or With Clause in SQL Server, also known as subquery refactoring or common table expressions(CTEs) is used for creating a temporary result set using a general SQL query, such that this temporary set can further be used multiple times within the main SELECT, INSERT, UPDATE or DELETE statements, i.e, SQL WITH clause creates a temporary virtual table with can be further used in main SQL queries.
--Define the CTE(Temporary Table)name andcolumn list
--Define the CTE query
--Define the main query
There are different parameters used in the syntax are :
WITH: This With clause is used for the purpose of creating a common table expression or temporary tables
Temp_TableName ( ColumnName1, ColumnName2, …): Here, Temp_TableName is the name of CTE, and ( ColumnName1, ColumnName2, …) is the definition of column names of the CTE which we will be using further in the main query.
AS (SELECT ColumnName1, ColumnName2 FROM TableName1 WHERE condition): This section specifies a SELECT statement whose result set will populate the CTE.
SELECT ColumnName1, ColumnName2 FROM Temp_TableName: This section specifies the main outer query. The SELECT statement will use the columns from the resultant CTE and produces the final result.
Which parameters are mentioned above, all the parameters are mandatory. You may use WHERE GROUP BY, ORDER BY, and HAVING clauses based on your requirement.
Important Note: A CTE can’t describe another CTE. But if more than one CTE then the definition is required we can use set operators like UNION, UNION ALL, INTERSECT, and EXCEPT.
Benefits of Using the WITH Clause
The SQL WITH clause permits you to reduce joins and logically sequence your code. Furthermore, it does this by creating temporary tables (i.e. technically they are views) that are usable by your main SQL query statement so that you can break your code into smaller & easier-to-understand snippets.
How Does SQL WITH Clause work and How Uses it?
WITH clause permits us to provide a subquery block a name that can be utilized in multiple places within the main SELECT, INSERT, DELETE or UPDATE SQL query. Furthermore, the name assigned to the subquery is treated as though it was an inline view or a table.
It is most helpful when you required the identical or same set of results data multiple times. In that case, you can generally define a CTE for this data and reuse the identical again and again by referencing it. It’s a kind of code reuse.
Going ahead we’ll be discussing the above-mentioned WITH clause in good detail.
In order to demonstrate and describe the WITH clause in SQL effectively, we’ll be using the following “Orders” table. Basically, this table is made for the purpose of an e-commerce website. This table contains Order _ID, Customer_Names, City, and the details of the items purchased by them.
The schema for the as per above mentioned “orders” table is:
Number of Records: 10
Order_ID (Primary key)
Let’s have a glance at the records in the orders table. in order that later, we can understand how
With Clause in SQL Server Helpful:
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Examples of With Clause in SQL Server
Here are a some examples to understand WITH clause in SQL.
Find out the average number of orders placed per month for every category of an item sold-out at the e-commerce website.
As above you can see that SQL WITH clause is used generally for creating temporary tables that can be used further in the main SQL query. Furthermore, it reduces the cost of joining operations and helps in reusing the same or equivalent piece of code again and again by referencing. The SQL WITH clause is very good when used with advanced or complex SQL statements rather than simple ones
It also allows you to break down complex SQL queries into smaller ones that make it simple for debugging & processing the most complex queries. The WITH clause in SQL Server is generally a drop-in replacement to the normal sub-query.