>>>>>A quick note: "Column = @Param OR @Param IS NULL" is not the same as "@Param IS NULL OR Column = @Param".
>>>>
>>>>Why? It is exactly the same.
>>>
>>>For MSSQL's sake, I hope it isn't!
>>>
>>>When the first condition is true, the second is not tested. So, in the second expression, if @Param IS NULL there is no need to check on Column's value.
>>
>>This is not how MS SQL works query optimizer works. The order of conditions makes absolutely no difference.
>
>Wow, it seems you're right.
>
>By any chance, the value of @Param can be changed during the SELECT?

No, the value of @Param is not going to change in SELECT unless you have it like this

select @param = [some column] from ...