Junior Set Operators SQL & Databases

Explain UNION vs UNION ALL.

Q: Explain UNION vs UNION ALL.

Short answer: UNION removes duplicates (extra sort/distinct cost). UNION ALL keeps all rows and is faster when duplicates are impossible or acceptable. Default to UNION ALL unless you truly need distinct.

Short answer: UNION removes duplicates (extra sort/distinct cost). UNION ALL keeps all rows and is faster when duplicates are impossible or acceptable.

Default to UNION ALL unless you truly need distinct.

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