What's the difference between NOT EXISTS vs. NOT IN vs. LEFT JOIN WHERE IS NULL?

Question

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          


        

Answer 1

• NOT IN vs. NOT EXISTS vs. LEFT JOIN / IS NULL: SQL Server

• NOT IN vs. NOT EXISTS vs. LEFT JOIN / IS NULL: PostgreSQL

• NOT IN vs. NOT EXISTS vs. LEFT JOIN / IS NULL: Oracle

• NOT IN vs. NOT EXISTS vs. LEFT JOIN / IS NULL: MySQL

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.