In SQL Null is not a value… not a value!
I have been spending a lot of time fixing SQL Server database errors caused by stored procedures attempting to compare null. If you don’t know, in SQL:
NULL = NULL is false NULL <> NULL is false
Null is not a value. Null is nothing. You can’t compare nothing to nothing because there is nothing to compare. I know you can do a select and see the word NULL in the results in SQL Management Studio, but that is just a marker so you don’t confuse empty strings with NULL or something.
If you need to do a comparison on a nullable value please check that shit for null first:
t2.column2 is null or t2.column2 = t1.column2 t2.column2 is not null
Also, if you try to be smart and turn ANSI_NULLS off you are going to be hurt when you have to upgrade your SQL Server to a version that forces ANSI_NULLS on (it’s coming).
I have been guilty of comparing NULL and saying, “it has a NULL value.” Now that I am having to fix scripts written by someone who did think about NULL, I wanted to rant and hammer this point home for myself so I don’t cause anyone the pain I am feeling right now. Null is not a value… not a value!