On Tue, Mar 22, 2011 at 06:25:04PM +0700, Dan Kennedy scratched on the wall:
> SQLite assumes that the result of each expression in the WHERE
> clause depends only on its inputs. If the input arguments are
> the same, the output should be do. Since random() has no inputs,
> SQLite figures that it must always return the same value.
To what degree? And expression like "...WHERE 20 <= (random()%100)"
has no "inputs" other than constants, but is still evaluated once per
row. Or is it just raw functions and column references, and not the
expression as a whole?
Either way, it would seem a function with no inputs should always be
considered non-constant. Unless someone writes a function that boils
down to func(){return VALUE;}, it is very likely the function
references some external value or state, and is unlikely to return
the same value.
I realize that most systems will only evaluates random() once, even
in a larger expression, but I've always found it nice that SQLite did
not in expressions like the one I gave. It makes it much easier to
sample data.
-j
--
Jay A. Kreibich < J A Y @ K R E I B I.C H >
"Intelligence is like underwear: it is important that you have it,
but showing it to the wrong people has the tendency to make them
feel uncomfortable." -- Angela Johnson
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