[snip]
Alan Nilsson wrote:
>
> On Oct 30, 2006, at 3:27 PM, Jay Blanchard wrote:
>
>> [snip]
>> I am trying to find records where the value of a filed is NULL. I
>> know that there are records that have null values but the result is
>> always an empty set.
>>
>> eg:
>> select test_id from tests where test_id=NULL
>>
>> always returns an empty set when there are in fact records that have
>> a null value for test_id. Is there some trick to finding null valued
>> records in MySQL? This same sql has always worked on any other dbms
>> I have used.
>> [/snip]
>>
>> Of course this will return an empty set because you have only
selected
>> the test_id, try this;
>>
>> SELECT * FROM tests WHERE test_id IS NULL
>
> Yes, that works, but I was also trying SELECT * instead of just the
key
> field (just a typo in the example). The problem was in the equal sign
> versus the 'IS' operator. Any reason why MySQL does not honor
> <field>=NULL? Seems kind of odd.
Sql standard says you use IS NULL.
[/snip]
And the reason for that is because nothing is actually equal to NULL.
For a field to be equal to NULL it would actually have to contain NULL,
in which case it would not be actually NULL.
