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⊘ -

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
  SELECT edges.* FROM edges
                 JOIN path 
                   ON edges.a = path.b
  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.

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