intermediate~2h
Set Operators — UNION, INTERSECT, EXCEPT/MINUS
SQL's set operators combine the results of two queries by set logic rather than by joining columns — the right tool whenever the question is really "which rows are in either, both, or only one of these two result sets."
Learning objectives
- State precisely what UNION, UNION ALL, INTERSECT, and EXCEPT each keep and discard.
- Explain why UNION ALL is cheaper than UNION, in terms of what work the database skips.
- Recognize when a set operator is the right tool versus when a JOIN actually answers the question.
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Set Operators — UNION, INTERSECT, EXCEPT/MINUS