Mike Conley wrote: > On Tue, Dec 22, 2009 at 2:34 AM, jo <jose.soa...@sferacarta.com > <mailto:jose.soa...@sferacarta.com>> wrote: > > Hi all, > > I'm trying to solve this error... > > File > "/home/sfera/release/sicer/BASE/controller/controlli/sopralluogo.py", > line 645, in verifiche > Piano.c.data_inizio <=data.get('data_sop') , > File "/usr/lib/python2.4/site-packages/sqlalchemy/sql.py", line > 1294, in > __le__ > return self._compare('<=', other) > File "/usr/lib/python2.4/site-packages/sqlalchemy/sql.py", line > 1423, in > _compare > raise exceptions.ArgumentError("Only '='/'!=' operators can be > used with > NULL") > ArgumentError: Only '='/'!=' operators can be used with NULL > > ------------------------------------- > > here the code that originates the above error: > > sr = sa.and_(Piano.c.data_inizio <=data.get('data_sop') ) > > I suppose data.get('data_sop') returns a None value, thus, sa compiles > the query like so: > > where piano.data_inizio <= NULL > > Could someone give me, some suggest how to solve this problem? > Thank you > > > This is correct behavior for a SQL query since the only legal > behavior for NULL is IS NULL or IS NOT NULL. > > First question to answer is what should your application do when > data_sop is NULL? > If you want to treat NULL same as zero, use a case() function to force > null to zero in the comparison. If NULL should not participate at all, > put a "!=None" check first in the and_condition to skip rows with NULL > values. There are probably other alternatives, but it all comes down > to desired behavior when the column is NULL. Thank you, for the clue, Mike. j
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