Avoiding execution of some functions by query rewriting

Hello,

I would like to allow the execution of a function (my_function) only if its argument (my_table.x) belongs to a predefined interval (e.g. [100,1000]).

Let's take the following query example :

(q)  SELECT * FROM my_table WHERE my_function(mytable.x);

I would like this query automatically rewrites itself to check whether "mytable.x" belong to the interval [100,1000] :

(q')  SELECT * FROM my_table WHERE (my_table.x BETWEEN 100 AND 1000) AND my_function(my_table.x);

The command EXPLAIN ANALYSE shows that the second query is really faster than the first one.

How can I change the query execution plan in order to automate the process of query rewriting (q into q') ?

Where can I store suitably the metadata about the interval [100,1000] associated to my_function ?

 

Thanks by advance,

Thomas Girault