The second form of your query will work if you make your mark your function as deterministic, meaning that for a given set of input values, it will always return the same result.
With that set, Oracle will only run the conversion once for each parameters in the where clause rather than for every row.
With this:
CREATE OR REPLACE FUNCTION TO_MINUTE_D (DATE_IN IN DATE)
RETURN NUMBER DETERMINISTIC AS
BEGIN
/* Minute 0 = 12/30/1899 12:00am */
RETURN
(TRUNC(DATE_IN, 'DD') - TO_DATE('12/30/1899', 'MM/DD/YYYY')) * 1440 +
TO_NUMBER(TO_CHAR(DATE_IN, 'HH24')) * 60 +
TO_NUMBER(TO_CHAR(DATE_IN, 'MI'));
END TO_MINUTE_D;
/
On a table filled with a large bunch of dummy rows (increasing ints), I get the following timings consistently:
SQL> SELECT * FROM MY_TABLE
WHERE START_MINUTE < TO_MINUTE(TO_DATE('2013-01-31', 'YYYY-MM-DD'))
AND STOP_MINUTE > TO_MINUTE(TO_DATE('2013-01-01', 'YYYY-MM-DD'));
no rows selected
Elapsed: 00:00:12.69
versus deterministic-annotated function:
SQL> SELECT * FROM MY_TABLE
WHERE START_MINUTE < TO_MINUTE_D(TO_DATE('2013-01-31', 'YYYY-MM-DD'))
AND STOP_MINUTE > TO_MINUTE_D(TO_DATE('2013-01-01', 'YYYY-MM-DD'));
no rows selected
Elapsed: 00:00:00.07
You should get very close to what you have with the values plugged in directly, and indexes on those columns can be used as if you'd plugged in literals.
(Putting the conversion function on the start|stop_minute columns isn't a good idea in general as you've discovered, unless you have a function-based index on those that matches exactly.)
Well, there is the Postgres extension plpgsql_check, successor of plpgsql_lint:
plpgsql_check is next generation of plpgsql_lint. It allows to check
source code by explicit call plpgsql_check_function.
I'm not currently using either, but the author Pavel Stehule is one of the core developers of PL/pgSQL (and also active around here).
Pavel announced it Dec. 2013 in this blog post.
Best Answer
There's a different, simpler, solution for this. Add an argument to function
fAwith a default value, for instance:called_from_b BOOLEAN DEFAULT FALSE. Then, provide that argument when callingfAfromfB.I understand that this doesn't directly answer your question, but it does provide a solution for the example usecase that you provide.