✅ Common Table Expressions in SQL 👇

What is a common table expression (CTE)?

CTEs are short lived.

CTEs are virtual tables which are created during the execution of a query, used by the query, and eliminated after query execution.

Syntax of CTE

Syntax of a CTE. Image by Author.

CTE can be can referenced within a SELECT, INSERT, UPDATE, or DELETE statement.

Two types of CTE

An example of a non-recursive CTE.

In MySQL and PostgreSQL, the RECURSIVE keyword is required.

An example to Recursive CTE to generate the numbers from 1 to 5.

When to Use CTEs

Error Message - "Cannot perform an aggregate function on an expression containing an aggregate or a subquery."

CTE vs. Sub-queries

Multiple References of a CTE. Image by Author.
Readability with a CTE in Multiple Tables Scenario. Image by Author.

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