[nalgeon]

WITH RECURSIVE is supported in MariaDB 10.2+, MySQL 8.0+, PostgreSQL 8.4+ and SQLite 3.8+. Oracle 11.2+ and SQL Server 2005 support recursive queries, but without the RECURSIVE keyword.

[dspillett]

Before recent versions, in the Postgres implementation CTEs were a wall to predicate push-down which can make them much less efficient than in other DBMSs. Worth noting if you need to support older versions for any reason.

[jeltz]

Yeah, but recursive CTEs are a different beast and still do not support pushdown. I am not sure if any database supports pushdown into recursive CTEs.