On Wed, Jan 07, 2009 at 08:12:44PM +0530, Nikhil Sontakke wrote: > Hi, > > Consider the following with latest CVS sources: > > postgres=# create table temp(val float4); > CREATE TABLE > postgres=# insert into temp values (415.1); > INSERT 0 1 > postgres=# select * from temp where val = 415.1; > val > ----- > (0 rows) > > !? > > The reason seems to be that 415.1 ends up being treated as a numeric and is > converted into float8 (why not float4? - it could have helped to use the > float4eq function then) > > The float8in function uses strtod which for some reason converts '415.1' > into 415.10000000000002 causing the subsequent comparison to fail. I guess > there are ample cases of float/strtod weirdness around? Needless to mention, > I was mighty surprised on seeing the output for the first time around :) > > Casting to float4 works as expected: > postgres=# select * from rel where x = 415.1::float4; > x > ------- > 415.1 > (1 row) > > Regards, > Nikhils > -- > http://www.enterprisedb.com
The traditional approach to equality test with floating point is to do the check plus-or-minus some value epsilon. Otherwise, such seemingly bizarre behavior results. Cheers, Ken -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
