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

<p><font size="2">Hi Steve,<br /><br /> > I believe count will only count not-null anyway<br /> > so this will
alwaysreturn zero.<br /><br /> Understood.  But that doesn't help me...<br /> What I need is a query expression that I
cansubstitute<br /> for isblabla below:<br /><br />   select maf<br />     from gallo.sds_seq_reg_shw<br />    where
mafisblabla;<br /><br /> Regards,<br /><br /> Tena Sakai<br /> tsakai@gallo.ucsf.edu<br /><br /><br /> -----Original
Message-----<br/> From: Steve Crawford [<a
href="mailto:scrawford@pinpointresearch.com">mailto:scrawford@pinpointresearch.com</a>]<br/> Sent: Tue 6/30/2009 3:39
PM<br/> To: Tena Sakai<br /> Cc: pgsql-sql@postgresql.org<br /> Subject: Re: [SQL] it's not NULL, then what is it?<br
/><br/> ...<br /> ><br /> ><br /> >   canon=# select count(maf) from gallo.sds_seq_reg_shw<br /> >  
canon-# where maf ISNULL;<br /> >    count<br /> >   -------<br /> >        0<br /> >   (1 row)<br />
><br/> I believe count will only count not-null anyway so this will always<br /> return zero. Try count(*) instead
ofcount(maf). Here's an example:<br /><br /> steve@[local]=> select * from barr;<br /> LOG:  duration: 0.226 ms<br
/> a | b<br /> ---+---<br />  a | b<br />  c | d<br />    | e<br /> (3 rows)<br /><br /> steve@[local]=> select
coalesce(a,'a is null'), coalesce(b, 'b is<br /> null') from barr;<br /> LOG:  duration: 0.283 ms<br />  coalesce  |
coalesce<br/> -----------+----------<br />  a         | b<br />  c         | d<br />  a is null | e<br /> (3 rows)<br
/><br/> steve@[local]=> select count(a) from barr;<br /> LOG:  duration: 0.339 ms<br />  count<br /> -------<br />
    2<br /> (1 row)<br /><br /> steve@[local]=> select count(*) from barr where a isnull;<br /> LOG:  duration:
0.350ms<br />  count<br /> -------<br />      1<br /> (1 row)<br /><br /><br /><br /></font>