Appendix Set theory basics and SQL operations: UNION, INTERSECT, EXCEPT

264. Set theory basics and SQL operations: UNION, INTERSECT, EXCEPT

One of the most underrated features of SQL is the set operators: UNION, EXCEPT and INTERSECT.

IMO in some cases set operators are much more readable then joins. For example, when we need to get records that appear in both tables. Yep, it’s a job for the INNER JOIN. But it our tables have only one column (just list of emails returned by a view or subquery) then I’d vote for the set operators. Let’s look at some examples.

UNION

UNION operators combines two sets (read tables or query results) together. We’ve used it already to create virtual tables:...

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