Interview Q&A / PostgreSQL
PostgreSQL interview questions
Indexes, EXPLAIN, transactions and isolation, JSONB and the Postgres specifics backend interviews probe.
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- Should a recursive CTE use UNION or UNION ALL?
UNION ALL keeps every produced row and is faster. UNION removes duplicates against all rows found so far, which can stop some cycles but costs extra work. For trees, use UNION ALL; for graphs with possible loops, add explicit cycle protection.
IntermediateQuick answer1 min read