“<>” vs “NOT IN”

Question

I was debugging a stored procedure the other day and found some logic something like this:

SELECT something
FROM someTable
WHERE idcode <> (SELECT ids          


        

Answer 1

<> is a "singular" NOT operation; NOT IN is a set operation, so it makes sense that the former wouldn't work. I have no idea whether or not it may have done so under a previous version of SQL Server, however.