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Home -> Community -> Mailing Lists -> Oracle-L -> RE: to_number question
sorry -- couldn't chime in any earlier in this thread -- what a pity ;-)
I hope I am not just repeating someone else here
parenthesis don't really impose any processing order;
they just scope the operations in your expressions.
"(A or B) and C" is obviously not the same as "A or (B and C)", because they have different truth tables. however, consider the following:
"(A or B) and C" is logically equivalent with "(A and C) or (B and C)" "A or (B and C)" is logically equivalent with "(A or B) and (A or C)"
so any optimizer would have the right to use the above two transformations
in their attempt to come back with a good plan; that is, the order in which
the predicates A, B, and C are visited is unpredictable and should be 100%
free,
regardless any parentheses.
Kind regards,
Lex.
-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Stephen.Lee_at_DTAG.Com
Sent: Friday, July 16, 2004 15:39
To: oracle-l_at_freelists.org
Subject: RE: to_number question
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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