I want to confirm that a behavior I'm observing in ODB 2.2.28 is actually
intended to work the way it appears to be, and that this behavior will be
maintained.
I'm doing an UPDATE that relies on "short-circuit evaluation" of the WHERE
clause:
UPDATE Cache CONTENT {"instance":"XYZ", "key":"JJJ", "aaa":5454, "bbb":2323,
"ccc":5353, "expires": 999} UPSERT WHERE (instance="XYZ" AND key="JJJ") OR
expires <= 1000
There are indexes on (instance, key) and on (expires). This statement will
do the following:
1) Update the existing record where instance=XYZ and key=JJJ.
2) Update the existing record where expires<=1000.
3) Insert a new record (if both "parts" of the WHERE clause fail).
As I said, this does work just as I described, but as you can see it relies
on the order of the logic in the WHERE clause. If the SQL optimizer chose
to look at the expires<=1000 first, then it might do #2 instead of #1
(although that would cause an index violation on (instance, key), assuming
that record already exists.
Bottom line, my question is simply "does the SQL optimizer do short-circuit
evaluation of the WHERE clause in the left-to-right order as presented" (or
have I just gotten lucky in my testing)? And if not, is there a way to
ensure that it does?
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