NULL values in where clause

Question

i\'ve got a table \"bla\" like this:

[id]    [name]    [fk]
1       test      4
2       foo       5
3       bar       NULL

if i do the sql

Answer 1

NULL is not a value, but rather the unknown absence of a value. If you'd like to test for NULL, you have to do so explicitly by using IS NULL and IS NOT NULL. For example, NULL will test FALSE even against NULL itself. So, working with NULL is only done with the aforementioned functions (and ISNULL()). Your query could be rewritten as

SELECT * FROM bla WHERE fk <> 4 OR fk IS NULL