Re: RE: counting distinct rows on more than one column

If the fields are fixed length character type, then the simpler
concatenation should work.

Actually, the requirement is only that all but the final field be fixed
length.

And if they aren't fixed length, you can cast them to be such, as long as
you know the maximum length of the string values, as in the following where
that maximum is 20 and we are looking at 3 fields:

select count(distinct (cast(field1 as char(20)) || cast(field2 as char(20))
|| field3)) from ...

Jim Ballard

----- Original Message -----
From: "Jeff Eckermann" <jeckermann@verio.net>
To: "'Dirk Lutzebaeck'" <lutzeb@aeccom.com>; "Michael Fork"
<mfork@toledolink.com>
Cc: <pgsql-sql@postgresql.org>
Sent: Wednesday, March 28, 2001 3:43 PM
Subject: [SQL] RE: counting distinct rows on more than one column


> I don't think this will necessarily work:
>
> field1 | field2
> aa     |  ab
> a       |  aab
>
> These are two distinct rows, so should be counted as two.
> The proposed method would count them as one.
> You can get around this problem by doing:
> count (distinct (a || x || b))
> where x is some character not found in your data.
>
> > -----Original Message-----
> > From: Dirk Lutzebaeck [SMTP:lutzeb@aeccom.com]
> > Sent: Wednesday, March 28, 2001 1:32 PM
> > To: Michael Fork
> > Cc: pgsql-sql@postgresql.org
> > Subject: Re: counting distinct rows on more than one column
> >
> > Michael Fork writes:
> >  > In 7.0.3, I believe the following would work:
> >  >
> >  > SELECT count(distinct(a || b)) FROM t;
> >
> > Great, this works! I don't quite get it why...
> >
> > Dirk
> >
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