Another SQL set operation, UNION ALL, is almost the same as UNION, but will not eliminate duplicates.
As with the other topics we’ve covered in this series, there is a wealth of information available on the topic of sets, databases, and SQL.
Check out this great read on Set Theory and SQL: “SQL-99 Complete, Really”, by Peter Guzman & Trudy Pelzer hosted on MariaDB
The link above contains more than just UNION, INTERSECT and EXCEPT, but there is a section towards the end that applies those operations to the larger discussion. This is a wonderful article!
Other good reads about Set Operations include:
Union and Union All:
See all of the SQL used in Querying Relational Databases in the Querying Relational Databases Cheat Sheet.
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