If you are experienced in Oracle, this might be confusing since Oracle
treats empty string and NULL as being the same.
> On Mon, 13 Oct 2003, Robert Partyka wrote:
>
>> why such condition:
>> foofield not like '%bar%'
>>
>> where foofield is varchar
>>
>> returns false (or rather even ignore row) on record where foofield is
>> null
>
> Actually, it probably returns unknown(NULL) on such records.
> NULL LIKE '%bar%' is unknown, so
> NULL NOT LIKE '%bar%' is also unknown.
>
> This is because NULL isn't the same as empty string, nor is it the
> absence of a value, but it's an unknown value.
>
> ---------------------------(end of broadcast)---------------------------
> TIP 6: Have you searched our list archives?
>
> http://archives.postgresql.org