where not exists?

Is null vs not exists?
The NULL is considered and returned by the NOT IN command as a value. The SQL NOT EXISTS command is used to check for the existence of specific values in the provided subquery. The subquery will not return any data; it returns TRUE or FALSE values depend on the subquery values existence check. Sep 22, 2017
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Where and where not exists in SQL?
The SQL NOT EXISTS Operator will act quite opposite to EXISTS Operator. It is used to restrict the number of rows returned by the SELECT Statement. The NOT EXISTS in SQL Server will check the Subquery for rows existence, and if there are no rows then it will return TRUE, otherwise FALSE.
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Where Not Exists vs LEFT JOIN?
EXISTS and NOT EXISTS both short circuit - as soon as a record matches the criteria it's either included or filtered out and the optimizer moves on to the next record. LEFT JOIN will join ALL RECORDS regardless of whether they match or not, then filter out all non-matching records. Jul 21, 2011
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Where Not Exists vs where not in?
The most important thing to note about NOT EXISTS and NOT IN is that, unlike EXISTS and IN, they are not equivalent in all cases. Specifically, when NULLs are involved they will return different results. To be totally specific, when the subquery returns even one null, NOT IN will not match any rows. Feb 18, 2010
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