hi this is not really a problem i just want to understand why:
in postgres 9
this_.lastModified<=NULL
evaluates to true, why? lastModified is a timestamp without timezone
i think it would be more logic to interpret it like "this_.lastModified<=0" which should evaluate to false if 0 is the lowest date and lastModified is a normal date
the complete query looks like this
select
this_.*
from Entity this_
inner join DEntity d2_ on this_.device=d2_.id
inner join u u1_ on this_.learner=u1_.userID
inner join LMEntity m3_ on this_.method=m3_.id
where u1_.userID='XXXX' and not (d2_.hardwareID='muh' and this_.timestamp='2013-08-02 00:00:00' and m3_.id=0 and this_.lastModified<=NULL)
this_.lastModified<=NULL always evaluates to null and in this case your where clause is effectively:
where u1_.userID='XXXX' and not (d2_.hardwareID='muh' and this_.timestamp='2013-08-02 00:00:00' and m3_.id=0 and null)
if all of the comparisons here:
d2_.hardwareID='muh' and this_.timestamp='2013-08-02 00:00:00' and m3_.id=0
evaluates to 'true' the this whole clause evaluates to true:
where u1_.userID='XXXX' and not (true and null)
true and null evaluates to null
where u1_.userID='XXXX' and not null
not null evaluates to null
where u1_.userID='XXXX' and null
if u1_.userID='XXXX' equal true, u1_.userID='XXXX' and null evaluates to null
and where null is equal to where false.
In short, the whole
where u1_.userID='XXXX' and not (d2_.hardwareID='muh' and this_.timestamp='2013-08-02 00:00:00' and m3_.id=0 and this_.lastModified<=NULL)
will evaluate to null if u1_.userID='XXXX' and all of d2_.hardwareID='muh' and this_.timestamp='2013-08-02 00:00:00' and m3_.id=0 gives true
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