That s what you said. So first exlude them, then join tables.
Adomas

>>>Actually, there are a lot of nulls. What there isn't, is a lot of
>>>duplicate values once nulls are excluded.

Rick Debay wrote:

>>As you said, there are only few values not null, so first, i think you
>>
>>
>should cut off null rows, then ask for
>
>
>>join. optimizer "should" be told to make such steps : 1. filter nulls
>>
>>
>2. join. (ps. 2.1. t1.a = t2.b is same
>
>
>>as t2.a =t1.b, because same table) So, your query ( or its variations)
>>
>>
>would be 1.
>
>
>>Select
>> *
>>From
>> tbl t1
>>Where
>>t1.a is not null and t1.b is not null
>>
>>
>
>Actually, there are a lot of nulls. What there isn't, is a lot of
>duplicate values once nulls are excluded.
>
>-----Original Message-----
>From: firebird-support@yahoogroups.com
>[mailto:firebird-support@yahoogroups.com] On Behalf Of Adomas
>Urbanavicius
>Sent: Tuesday, November 15, 2005 12:52 PM
>To: firebird-support@yahoogroups.com
>Subject: Re: [firebird-support] Long query help
>
>As you said, there are only few values not null, so first, i think you
>should cut off null rows, then ask for join. optimizer "should" be told
>to make such steps : 1. filter nulls 2. join. (ps. 2.1. t1.a = t2.b is
>same as t2.a =t1.b, because same table) So, your query ( or its
>variations) would be 1.
>
>Select
> *
>From
> tbl t1
>Where
>t1.a is not null and t1.b is not null
>and
> exists (
> select 1
> from tbl t2
> where (t2.a = t1.b
>/////// and t2.a is not null and t1.b is not null) /// this is
>not found already as nulls ommited from first condition
>/////// or (t2.b = t1.a and t2.b is not null and t1.a is not null)
>////// if t2.a = t1.b, so in reverse would be found anyway
> )
>
>
>
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