That means only one thing, the condition is always wrong.
The right question here would be "Why do we use it?"
This is a tuning technique to make it a stage 2 predicate and to force an access path.
ex. if there are two indexes on the table and you are qualifying the sql with both the columns, the optimizer might choose any of these indexes. But, when you add OR 1=0 (or 0<>0 in this case) to one of the predicates, it will force the optimizer to take the other index.
Joined: 20 Oct 2006 Posts: 6970 Location: porcelain throne
the easiest way to see the effect of the 0<>0 is to
take the query into spufi, run explain,
modify the query (removing the 0<>0), run another explain (different plan number),
and compare the two explain outputs.
since you omitted part of the where clause,
we really don't know the effect of the additional predicate (0<>0),
other than knowing we have a stage 2 predicate.
As Bharath Bhat said, the effect is to disable the use of the index by the optimizer
forcing either a table space scan or use of another index mentioned in the where clause (which you have omitted).