Re: SQL use of OR and parens

On 9/28/2015 4:44 PM, Dan Rasch wrote:

Is there any difference in these two statements:

SELECT PLNITM, PLNSTR, PLNCDT as EFF_DATE,
PLNAMT, PLNADT,
FROM PFILE WHERE
WHERE PLNCDT > 150901 AND PLNITM = 2090312 AND PLNSTR < 11
OR PLNSTR = 0 AND PLNITM = 2090312
OR PLNSTR > 78 AND PLNITM = 2090312

SELECT PLNITM, PLNSTR, PLNCDT as EFF_DATE,
PLNAMT, PLNADT,
FROM PFILE WHERE
WHERE PLNCDT > 150901 AND PLNITM = 2090312 AND PLNSTR < 11
OR (PLNSTR = 0 AND PLNITM = 2090312)
OR (PLNSTR > 78 AND PLNITM = 2090312)

I have typically not used the parens with no apparent harm.

They're the same as far as end results are concerned. You might see
optimiser differences without the parens.

This was surprisingly difficult to find in the SQL Reference. I was
looking for 'Operator precedence' or 'Order of operations' but these
aren't operations; they're search conditions for predicates. So:

Search conditions within parentheses are evaluated first. If the order
of evaluation is not specified by parentheses, NOT is applied before
AND, and AND is applied before OR. The order in which operators at the
same precedence level are evaluated is undefined to allow for
optimization of search conditions.

http://www-01.ibm.com/support/knowledgecenter/ssw_ibm_i_72/db2/rbafzch2srch.htm