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Editorial Team
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Asked: 2026-05-13T18:44:02+00:00

It seems to me that you can do the same thing in a SQL

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It seems to me that you can do the same thing in a SQL query using either NOT EXISTS, NOT IN, or LEFT JOIN WHERE IS NULL. For example:

SELECT a FROM table1 WHERE a NOT IN (SELECT a FROM table2)

SELECT a FROM table1 WHERE NOT EXISTS (SELECT * FROM table2 WHERE table1.a = table2.a)

SELECT a FROM table1 LEFT JOIN table2 ON table1.a = table2.a WHERE table1.a IS NULL

I’m not sure if I got all the syntax correct, but these are the general techniques I’ve seen. Why would I choose to use one over the other? Does performance differ…? Which one of these is the fastest / most efficient? (If it depends on implementation, when would I use each one?)

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1 Answer

  1. Editorial Team

    In a nutshell:

    NOT IN is a little bit different: it never matches if there is but a single NULL in the list.

    • In MySQL, NOT EXISTS is a little bit less efficient

    • In SQL Server, LEFT JOIN / IS NULL is less efficient

    • In PostgreSQL, NOT IN is less efficient

    • In Oracle, all three methods are the same.

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