it's not NULL, then what is it? - Mailing list pgsql-sql

<p><font size="2">Hi Everybody,<br /><br /> I have a table called gallo.sds_seq_reg_shw,<br /> which is like:<br /><br
/>  canon=# \d gallo.sds_seq_reg_shw<br />        Table "gallo.sds_seq_reg_shw"<br />         Column      |  Type   |
Modifiers<br/>   ------------------+---------+-----------<br />    name             | text    |<br />   
response        | text    |<br />    n                | integer |<br />    source           | text    |<br />   
test            | text    |<br />    ref              | text    |<br />    value            | real    |<br />   
pvalue.term     | real    |<br />    stars.term       | text    |<br />    gtclass.test     | text    |<br />   
fclass.test     | text    |<br />    gtclass.ref      | text    |<br />    fclass.ref       | text    |<br />   
markerid        | integer |<br />    maf              | real    |<br />    chromosome       | text    |<br />   
physicalposition| integer |<br />    id               | text    |<br />    ctrast           | text    |<br />  <br /> I
amintereseted in the column maf (which is real):<br /><br />   canon=# select maf from gallo.sds_seq_reg_shw<br />  
canon-# order by maf asc;<br />        maf    <br />   -------------<br />    0.000659631<br />    0.000659631<br />   
0.000659631<br/>    0.000659631<br />         .<br />   (trunacated for the interest of breivity)<br />         .<br
/><br/> Another way to look at this column is:<br /><br />   canon=# select maf from gallo.sds_seq_reg_shw<br />  
canon-# order by maf desc;<br />        maf    <br />   -------------<br />              <br />              <br />
             <br/>         .<br />   (trunacated for the interest of breivity)<br />         .<br /><br /> These rows
shownare blanks, as far as I can tell.<br /> But...<br /><br />   canon=# select count(maf) from
gallo.sds_seq_reg_shw;<br/>    count<br />   -------<br />    67284<br />   (1 row)<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 />   canon=#<br />   canon=# select count(maf) from gallo.sds_seq_reg_shw<br />   canon-# 
wheremaf NOTNULL;<br />    count<br />   -------<br />    67284<br />   (1 row)<br /><br /> My confusion is that if
theyare real and not null,<br /> what are they?  How would I construct a query to do<br /> something like:<br /><br />
 selectcount(maf)<br />    from gallo.sds_seq_reg_shw<br />   where maf ISBLANK;<br /><br /> Thank you in advance.<br
/><br/> Regards,<br /><br /> Tena Sakai<br /> tsakai@gallo.ucsf.edu</font>