What is a FULL OUTER JOIN and when would you use it?

Short answer: A FULL OUTER JOIN returns all rows from both tables, matching rows where possible. If there's no match, the result will contain NULL values for the columns from the table that doesn't have a match. Use case: When you want to combine all records from both tables, regardless of whether they match, and include NULL where no match exists.

Example code

SELECT * FROM table1 FULL OUTER JOIN table2 ON table1.id = table2.id;

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1. Define — one clear sentence (the short answer above).
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