cast a null to integer (zero)

Hi,

i need to make an update statement that does something like:

update table set col = value + (select sum(col) where type = 'sometype') where .....etc

but there is trouble when the sub query "select sum(col) where type = 'sometype'" returns null - the update fails because:

set col = value + ()

is not valid.

how can i make sure that "select sum(col) where type = 'sometype'" returns a zero instead of null?

Thanks and regards,  Mike.
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meverestAsked:
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ravenplCommented:
(select coalesce(sum(col), 0) where type = 'sometype')

But note, that coalesce is in general CASE clause. Look into it.

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meverestAuthor Commented:
thanks for that tip - i will investigate and make sure that it is valid for my purpose...

will let you know shortly :)

earth man2Commented:
coalesce function takes the first non null argument as its result
try
update table set col = value + coalesce( ( select sum(col) from table_x where type = 'sometype' ),  0 ) where .....etc
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meverestAuthor Commented:
beaut!  it works like a gem.

not sure what you mean by your note about CASE - my reading of the docs suggests that coalesce function is exactly for this sort of situation...

are you warning of some performance hit using these functions?

thanks again!

Mike.
meverestAuthor Commented:
oh, thanks earthman2 as well - didn't notice your comment until i had responded to the earlier one.

ravenplCommented:
I meant, that Coalesce is just CASE clause, but nicely called.
Details here:
http://www.postgresql.org/docs/8.0/static/functions-conditional.html#AEN12056
meverestAuthor Commented:
OK, i think i get your meaning.  yet it still seems to me that even though coalesce is like a shorthand version of an equivalent case, it is a fairly specific case (no pun intended)

that is a CASE could be used in place of coalesce, but coalesce may not necessarily substiute a coalesce.

but nonetheless, now I have learned TWO new useful tricks with postgreSQL :) :)

Cheers!
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