TSQL - Faster to use IN (list) or use NOT IN (list) for a small list?

sql tsql sqlperformance notin sql-in
johntrepreneur picture johntrepreneur · Jul 12, 2013 · Viewed 10.1k times · Source

One of my columns can only contain 4 possible values (val1, val2, val3, val4).

I need to add an additional filter in the WHERE clause to exlude one of those 4 values (i.e. val4).

Is it going to be faster to use NOT IN ('val4') or IN ('val1','val2','val3')?

Answer

Cᴏʀʏ picture Cᴏʀʏ · Jul 12, 2013

NOT IN ('val4') is basically equivalent to

WHERE
    NOT (column = 'val4') /* or column <> 'val4' */

whereas IN ('val1', 'val2', 'val3') is basically equivalent to

WHERE
(
   column = 'val1'
   OR
   column = 'val2'
   OR 
   column = 'val3'
)

I would hope that the first option is faster, if only negligibly. The SQL engine might optimize IN differently depending on how many values you specify in the IN function and what indexes are available on your table. What behavior are you seeing that you're questioning the method to use?

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