Why does this query return different results when in a stored procedure?

Question

Synopsis

I\'ve got a query with a WHERE clause that contains a condition that checks a NULLable column against a parameter that may be NULL, like so:

Answer 1

Try altering the stored procedure in a session after setting ANSI_NULLS to ON.

SET ANSI_NULLS ON
GO

alter procedure procedureName 
...

From the docs:

For stored procedures, SQL Server uses the SET ANSI_NULLS setting value from the initial creation time of the stored procedure. Whenever the stored procedure is subsequently executed, the setting of SET ANSI_NULLS is restored to its originally used value and takes effect. When invoked inside a stored procedure, the setting of SET ANSI_NULLS is not changed.