Can I use… with recursive (… union [distinct] …)


2005200720092011201320152017201910.15.2.0Apache Derby2.0BigQuery11.5Db2 (LUW)1.4.200H210.2MariaDB8.0.118.0.128.0.16MySQL19cOracle DB8.4PostgreSQL2019SQL Server3.8.3SQLite

Union [distinct] within with recursive can be used to omit duplicate rows and thus preventing infinite loops.

WITH RECURSIVE path (from, to) AS (
   SELECT from, to
     FROM edges
    WHERE id = ?
UNION [DISTINCT]
   SELECT from, to
     FROM path
     JOIN edges ON edges.from = path.to
) …

The example properly terminates even if the graph stored in the edges table has cycles.

Normative References

The with recursive clause is defined in ISO/IEC 9075:2016-2 as part of optional feature T131. Union [distinct] belongs to mandatory feature E071-01.

About the Author

Photo of Markus Winand

Markus Winand is the SQL Renaissance Ambassador. He is on a mission to introduce developers to the evolution of SQL in the 21st century. Markus can be hired as trainer, speaker and consultant via winand.at.

Buy his Book on Amazon

Cover of “SQL Performance Explained”: Squirrel running on grass

The essence of SQL tuning in 200 pages

Buy on Amazon
(paperback only)

Paperback and PDF also available at Markus’ store.

Hire Markus

Markus offers SQL training and consulting for developers working at companies of any size.
Learn more »

Connect with Markus Winand

Markus Winand on LinkedInMarkus Winand on XINGMarkus Winand on Twitter
“modern SQL” by Markus Winand is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 Unported License.
Legal | Contact | NO WARRANTY | Trademarks | Privacy and GDPR | CC-BY-NC-ND 3.0 license