WITH clause must be defined before it’s used in the query.
Here is the basic syntax of a SELECT statement with the optional WITH clause:
Query syntax
WITH clause
The WITH clause provides a way to write supplemental statements for a larger query. These statements, also known as Common Table Expressions or CTEs, can be viewed as defining temporary tables that exist just for one query.
It helps break down complicated and large queries into simpler, easily readable forms and proves especially useful when the subquery is executed multiple times. It computes the aggregation once and can then be repeatedly referenced by its name in the queries.
CTEs can reference each other and can be nested. The
Basic CTE examples:
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