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List:       sqlite-users
Subject:    Re: [sqlite] Why "select count(distinct f1,
From:       Max Vlasov <max.vlasov () gmail ! com>
Date:       2010-06-26 19:18:38
Message-ID: AANLkTinXEWfXhKzoOfN3ttepNn9_LoyhqjPsVPcNCekA () mail ! gmail ! com
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On Sat, Jun 26, 2010 at 7:27 AM, zhangzhenggui <zhangzhenggui@126.com>wrote:

> tbl_test maybe like this:
> create table tbl_test(f1, f2, f3);
>
> Now, I want to get the num of records which (f1, f2) are distinct.
>
> I try "select count(distinct f1, f2) from tbl_test", but error occur: SQL
> error: wrong number of arguments to function count()
>
>
> although, I can do like this, but I think it not very good :
> select count(1) from (select distinct f1, f2 from tbl_test);
>
>

If you know the type and the maximum range (in case of integer) you can do
the tricks like this

select count(distinct ((Value1 << 32) | Value2)) FROM TestTable

but I did quick text for a table consisting of thousands of integers, the
speed is similar to your another query that you called not very good. I
think both needs some temporary storage, so what you like aesthetically is
the best :)

Max
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