Re: it's not NULL, then what is it?

Hi Steve,

 > I believe count will only count not-null anyway
 > so this will always return zero.

 Understood.  But that doesn't help me...
 What I need is a query expression that I can substitute
 for isblabla below:

   select maf
     from gallo.sds_seq_reg_shw
    where maf isblabla;

 Regards,

 Tena Sakai
 tsakai@gallo.ucsf.edu


 -----Original Message-----
 From: Steve Crawford [mailto:scrawford@pinpointresearch.com]
 Sent: Tue 6/30/2009 3:39 PM
 To: Tena Sakai
 Cc: pgsql-sql@postgresql.org
 Subject: Re: [SQL] it's not NULL, then what is it?

 ...
 >
 >
 >   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)