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What does DISTINCT do and what is its cost?

Q: What does DISTINCT do and what is its cost?

**DISTINCT** removes duplicate rows from a result set by sorting or hashing — which adds cost on large sets. If duplicates come from a join, fixing the join or using `EXISTS` is often better than masking them with DISTINCT.

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DISTINCT removes duplicate rows from a result set by sorting or hashing — which adds cost on large sets. If duplicates come from a join, fixing the join or using EXISTS is often better than masking them with DISTINCT.

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