I think at the heart of the argument that the error should not occur (at
least MY opinion) is that we CAN impose an order on processing so that (A or
B) and C is not the same as A or (B and C), and the RDBMS is not allowed to
throw away the parenthesis and do the processing in any way it chooses.
So at least some folk around here don 't like the fact that it is OK for the
RDBMS to "throw away the parenthesis " in the case of a subquery when an
optimizer that is too smart for its britches can form a logically equivalent
query ... assuming no errors occur.
Maybe it 's a purely pragmatic thing based on what gives the best performance
most of the time. Whatever the reason, I haven 't been convinced that it has
any basis in relational theory. It seems to be nothing more than a
specification.
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