Where-Clause with function(entered static parameter)

Question

Hello,
I have no clue on the way to deal with this issue.
Basically, for performance, I removed a join with a table, and replaced it by a call to a function within the where clause. This function only convert the entered date into an id, in order to compare with the id in the selected table.
I knew (I think I'm right!!) that if I put a function into a where-clause, then the function is called at each row.
As the parameter of this function is a Discoverer parameter, and therefore, it's a static value, I wanted to know whether with Discoverer, there would be a way to convert the entered Discoverer parameter value into a constant that I could use within my where-clause.
To summarise, hete is the face of my query, at the moment:
SELECT myColumns
FROM myTables
WHERE thisID < myConvertedDate(:RefDate);
I would like to do this :
The User enters the :RefDate, I convert it and save the result into a constant.
Then, my query would look like :
SELECT myColumns
FROM myTables
WHERE thisID < myConstantFromDate;
I hope that my explanation is clear, and that one of you will be able to advise me.
Thanks,
Olivier

Answer 1

Hello Nigel,
I am not too sure that the function is called at each row. This is just my thought, from my "average" knowledge of SQL. We cannot run tkprof at the office, in order to get a better understanding.
And also, the fact that goes towards this direction is that, when I add the call to my function in the where-clause, I have the impression that the query runs more slowly than without the call.
I reckon that it would be great if the optimizer notices that the function is called with the same value, and returns always the same result.
Thanks for your comments,
Olivier