How Can I Combine Multiple CTEs, Including Recursive CTEs, in a Single SQL Query?

Combining Multiple CTEs in a Single SQL Query

It is possible to combine multiple CTEs in a single query by using the WITH keyword followed by each CTE definition. However, if any of the CTEs are recursive (rCTEs), you must also use the RECURSIVE keyword at the beginning of the statement.

For example:

WITH RECURSIVE
cte1 AS (
...
),
cte2 AS (
SELECT ...
UNION ALL
SELECT ...
),
cte3 AS (
...
)
SELECT ... FROM cte3 WHERE ...

In this example, cte1 is a non-recursive CTE, cte2 is a rCTE, and cte3 is another non-recursive CTE.

The order of the WITH clauses is irrelevant when using the RECURSIVE keyword. This means that you can reference a CTE that is later in the list.

In some cases, you may want to use non-recursive CTEs to simplify the query. For example, you could use a non-recursive CTE to create a temporary table that you can then use in other CTEs.

By using multiple CTEs in a single query, you can improve the performance and readability of your code.

The above is the detailed content of How Can I Combine Multiple CTEs, Including Recursive CTEs, in a Single SQL Query?. For more information, please follow other related articles on the PHP Chinese website!