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 special in that it represents an "unknown" value. This can't be compared to numbers (or any other value for that matter), hence the result -

Is NULL <> 4? The answer is - don't know. Is 4 different from an unknown value?

Try this instead:

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