Andrius,
see the explanation about that at
http://www.postgresql.org/docs/8.3/static/functions-comparison.html for
more details.
Cheers
Julo
Heikki Linnakangas wrote:
> Andrius Glozeckas wrote:
>>
>> I have a parent_type_id linking to group_type_id on the same table
>> (group_type). I am trying to get the groups with certain
>> parent_type_id (be
>> it null or 17) and the number of their children in the same query:
>>
>> SELECT g1.*, COUNT(g2.*)
>> FROM group_type g1 LEFT JOIN group_type g2 ON g1.group_type_id =
>> g2.parent_type_id
>> WHERE g1.parent_type_id = null GROUP BY g1.name, g1.type, g1.choice,
>> g1.multiple, g1.self_ref,
>> g1.group_type_id, g1.parent_type_id
>>
>> But this doesn't give me any results, although there are a few
>> records with
>> parent_type_id = null and one with 17. I have tried a simpler query:
>>
>> SELECT g1.*, g2.* FROM group_type g1 LEFT JOIN group_type g2 ON
>> g1.group_type_id = g2.parent_type_id WHERE g1.parent_type_id = null
>>
>> This again doesn't give me any results
>>
>> If I take the WHERE off, I get a list as expected with several
>> g1.parent_type_id = null
>
> Use the IS NULL operator, instead of "= NULL", for testing if a column
> is null: "WHERE gl.parent_type_id IS NULL". This is a basic SQL thing,
> not a bug.
>