What is the difference between EXISTS and IN, and JOIN?
Model answer
IN checks a value against a list or subquery result. EXISTS checks whether a correlated subquery returns any row and can stop at the first match. A join can return duplicates if there are many matches. Modern optimisers often treat them similarly, but NOT IN has a trap with NULLs, so NOT EXISTS is safer.
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SQL JOINs: INNER JOIN and LEFT JOIN Explained in the course SQL for Beginners: Learn Databases Step by Step.
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