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I have a query in SQL Server 2008R2 that I want to run against a computed column that in turn I am going to index - in order to speed things up.

The column is of type int right now.

I cannot get the syntax right.

alter table dbo.tOutput Add StateNew as State IN (0, 10)

I get an error

Incorrect syntax near the keyword 'IN'.

The query, coming from C# entity framework, should then later on use the index and - well - be fast.

The C# seems to be converted to the IN usage, the original is like this:

tOutput.Where(x => (x.State == 0) || (x.State == 10))

The generated SQL reads

.. FROM tOutput WHERE State IN (0, 10) ..
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I do not think that you want a computed column here. It looks like what you really need is a filtered index (introduced in SQL Server 2008), using WHERE [State] IN (0, 10) as the filter. Once this index is created, queries that have that same predicate should use this index. Please take a look at:

Just FYI: a computed column is an expression that needs to return a scalar value. State IN (0, 10) is not a scalar expression, which is why you are getting the error. You could modify it to be something like CONVERT(TINYINT, CASE [State] WHEN 0 THEN 1 WHEN 10 THEN 1 ELSE 0 END), but then indexing that will still include all rows. Using a filtered index will only include the matching rows, which will be smaller and faster :-).

  • Isnt a bit/bool a scalar value? I think the filtered index should work though, too. Did not think about it, since it does not work on a computed column, but in my case, the column is not computed. – Andreas Reiff Jan 9 '18 at 18:18
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    @AndreasReiff SQL Server does not have boolean type so ther can be no scalar boolean values. If the expression was modified to yield an INT or a BIT, it would be accepted, i.e.: .. ADD StateNew AS CASE WHEN State IN (0, 10) THEN 1 ELSE 0 END – ypercubeᵀᴹ Jan 9 '18 at 18:30
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    @AndreasReiff A bit value is a scalar value, BUT State IN (0, 10) does not return a value; it evaluates to a boolean true / false, which is similar, but not the same. For example, you can do IF (State IN (0, 10))... but you cannot do SELECT ([State] IN (0, 10)) AS [YesOrNo] FROM .... This is why I have the note in the "Just FYI" section showing how to represent this as a scalar expression for use in a computed column. But again, the filtered index is better than a non-filtered index on a computed column. – Solomon Rutzky Jan 9 '18 at 18:43
  • You can do that in PostgreSQL. ;) SELECT x IN (1,2) FROM ( VALUES (1),(2),(4) ) AS t(x); Having a boolean type is awesome! – Evan Carroll Jan 9 '18 at 18:47
  • @EvanCarroll interesting...thanks for mentioning :-) – Solomon Rutzky Jan 9 '18 at 18:52

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