MySQL WITH Common Table Expression (CTE)

In MySQL, every statement or query produces a temporary result or relation. A common table expression or CTE is used to name those temporary results set that exist within the execution scope of that particular statement, such as CREATE, INSERT, SELECT, UPDATE, DELETE, etc.

1. What is a CTE in MySQL?
2. Is CTE better than subquery?
3. What is CTE and why we use this in SQL?
4. Does MySQL 5.7 support clause?
5. Can I use CTE in MySQL?
6. How do I use two CTE in SQL?
7. Can I use CTE in stored procedure?
8. When should I use CTE?
9. Can you use CTE in subquery?
10. How do I select CTE in SQL?
11. How do you use CTE multiple times?
12. What is the difference between temp table and CTE?

What is a CTE in MySQL?

A common table expression (CTE) is a named temporary result set that exists within the scope of a single statement and that can be referred to later within that statement, possibly multiple times.

Is CTE better than subquery?

The performance of CTEs and subqueries should, in theory, be the same since both provide the same information to the query optimizer. One difference is that a CTE used more than once could be easily identified and calculated once. ... In an ideal world, the query optimizer would find the perfect execution path.

What is CTE and why we use this in SQL?

A Common Table Expression, also called as 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 about how to create and use CTEs from our SQL Server.

Does MySQL 5.7 support clause?

Derived Tables will work on both MySQL 5.7 and MySQL 8, while the WITH clause is not supported in MySQL 5.7.

Can I use CTE in MySQL?

In MySQL every query generates a temporary result or relation. In order to give a name to those temporary result set, CTE is used. A CTE is defined using WITH clause. Using WITH clause we can define more than one CTEs in a single statement.

How do I use two CTE in SQL?

To use multiple CTE's in a single query you just need to finish the first CTE, add a comma, declare the name and optional columns for the next CTE, open the CTE query with a comma, write the query, and access it from a CTE query later in the same query or from the final query outside the CTEs.

Can I use CTE in stored procedure?

According to the CTE documentation, Common Table Expression is a temporary result set or a table in which we can do CREATE, UPDATE, DELETE but only within that scope. That is, if we create the CTE in a Stored Procedure, we can't use it in another Stored Procedure.

When should I use CTE?

The CTE is preferred to use as an alternative to a Subquery/View. A sub-query is a query within a query. It is also called an inner query or a nested query. A sub-query is usually added in a where clause of the SQL statement.

Can you use CTE in subquery?

A CTE can reference itself, a subquery cannot. A CTE can reference other CTEs within the same WITH clause (Nest). A subquery cannot reference other subqueries. A CTE can be referenced multiple times from a calling query.

How do I select CTE in SQL?

You can also use a CTE in a CREATE a view, as part of the view's SELECT query. In addition, as of SQL Server 2008, you can add a CTE to the new MERGE statement. After you define your WITH clause with the CTEs, you can then reference the CTEs as you would refer any other table.

How do you use CTE multiple times?

6 Answers

1. Redefine the CTE a second time. This is as simple as copy-paste from WITH... through the end of the definition to before your SET .
2. Put your results into a #temp table or a @table variable.
3. Materialize the results into a real table and reference that.
4. Alter slightly to just SELECT COUNT from your CTE:

What is the difference between temp table and CTE?

Temp Tables are physically created in the tempdb database. These tables act as the normal table and also can have constraints, an index like normal tables. CTE is a named temporary result set which is used to manipulate the complex sub-queries data. ... This is also created in the tempdb database but not the memory.