SQL With - How to Use the WITH Statement/Common Table Expressions (CTE) in SQL Server - SQL Training Online

In this video, I introduce the SQL WITH statement (also known as Common Table Expressions or CTE) and show you the basics of how it is used.

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The SQL WITH Statement is called Common Table Expressions or CTE for short in SQL Server

The SQL WITH statement is used for 2 primary reasons:

1. To move Subqueries to make the SQL easier to read.

2. To do recursive queries in SQL

Today, I just want to talk about the subquery piece.

I first want to take a look at the Employee table in the SQL Training Online Simple Database.

select * from employee

To talk about the SQL WITH statement, I have to first talk about and show you a subquery.

select *

from

(

select * from employee

) a

So that is an example of a subquery.

But, we want to talk about the SQL WITH, which allows you to move the subquery up and make the SQL a lot easier to read.

Here is the same query using the WITH statement.

WITH cteEmployee (employee_number,employee_name,manager)

AS

(

select employee_number,employee_name,manager from employee

)

select *

from cteEmployee

You can see that we start with the WITH clause and then we can use any name we want to name our CTE. In this case, I use -cteEmployee-.

Then we need to specify the columns inside of parenthesis.

Next comes the AS clause.

And finally, we just SELECT from the cteEmployee table we created.

And, that-s it.

But, I want to take it a step further and join the cteEmployee CTE back to the Employee table and get the Manager-s name.

Here is an example of that.

WITH cteEmployee (employee_number,employee_name,manager)

AS

(

select employee_number,employee_name,manager from employee

)

select cte.employee_number

,cte.employee_name

,cte.manager

,e.employee_name as manager_name

from cteEmployee cte INNER JOIN employee e on cte.manager = e.employee_number

That-s it.

That is the basic introduction into the SQL WITH statement in SQL Server. Microsoft also has some good examples on this.

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