Add computed column with "IN" syntax
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:


Create Filtered Indexes
CREATE INDEX


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 :-).