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