with recursive (… union [distinct] …)


Apache DerbyBigQueryDb2 (LUW)H2MariaDBMySQLOracle DBPostgreSQLSQL ServerSQLite2009201120132015201720192021✓ 3.8.3 - 3.43.0⊘ 3.5.7 - 3.7.11⊘ 2008R2 - 2022✓ 8.4 - 16⊘ 8.3⊘ 11gR1 - 21c✓ 8.0.11 - 8.0.34⊘ 5.0 - 5.7✓ 10.2 - 10.11⊘ 5.1 - 10.1⊘ 2.0.204 - 2.2.220⊘ 1.4.191 - 1.4.200⊘ 9.7 - 11.5.8⊘ 2.0⊘ 10.15.1.3 - 10.16.1.1

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

WITH RECURSIVE path (a, b) AS (
  SELECT edges.* FROM edges
                WHERE a = 1
UNION
  SELECT edges.* FROM edges
                 JOIN path 
                   ON edges.a = path.b
)
SELECT *
  FROM path

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 9075-2:2023 §7.17 as part of optional feature T131, “Recursive query”. Union [distinct] belongs to mandatory feature E071-01.

You can’t catch up on 20 years of SQL evolution in one day. Subscribe the newsletter via E-Mail, Twitter or RSS to gradually catch up and to keep modern-⁠sql.com on your radar.

About the Author

Photo of Markus Winand

Markus Winand provides insights into SQL and shows how different systems support it at modern-sql.com. Previously he made use-the-index-luke.com, which is still actively maintained. Markus can be hired as trainer, speaker and consultant via winand.at.

Buy the Book

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

The essence of SQL tuning in 200 pages

Buy now!
(paperback and/or PDF)

Paperback also available at Amazon.com.

Hire Markus

Markus offers SQL training and consulting for developers working at companies of all sizes.
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