From: Steve Crawford <scrawford@pinpointresearch.com>
To: Tena Sakai <tsakai@gallo.ucsf.edu>
Cc: pgsql-sql@postgresql.org
Subject: Re: it's not NULL, then what is it?
Date: Tue, 30 Jun 2009 15:39:24 -0700
Message-ID: <4A4A941C.2060604@pinpointresearch.com> (raw)
In-Reply-To: <FE44E0D7EAD2ED4BB2165071DB8E328C04E84C01@egcrc-ex01.egcrc.org>
References: <FE44E0D7EAD2ED4BB2165071DB8E328C04E84C01@egcrc-ex01.egcrc.org>
...
>
>
> canon=# select count(maf) from gallo.sds_seq_reg_shw
> canon-# where maf ISNULL;
> count
> -------
> 0
> (1 row)
>
I believe count will only count not-null anyway so this will always
return zero. Try count(*) instead of count(maf). Here's an example:
steve@[local]=> select * from barr;
LOG: duration: 0.226 ms
a | b
---+---
a | b
c | d
| e
(3 rows)
steve@[local]=> select coalesce(a, 'a is null'), coalesce(b, 'b is
null') from barr;
LOG: duration: 0.283 ms
coalesce | coalesce
-----------+----------
a | b
c | d
a is null | e
(3 rows)
steve@[local]=> select count(a) from barr;
LOG: duration: 0.339 ms
count
-------
2
(1 row)
steve@[local]=> select count(*) from barr where a isnull;
LOG: duration: 0.350 ms
count
-------
1
(1 row)
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To: pgsql-sql@postgresql.org
Cc: scrawford@pinpointresearch.com, tsakai@gallo.ucsf.edu
Subject: Re: it's not NULL, then what is it?
In-Reply-To: <4A4A941C.2060604@pinpointresearch.com>
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