SQL plan in functions

Hello, list.

I have a function witch returns record set. What troubles me is that
depending on parameters I pass to this function  the execution time
varies greatly. On the other hand if I execute the query (not the
function) with pgAdmin  - it gives results quickly.
In previous post You helped me realize, that the problem was because the
function has only one plan of SQL inside no matter the parameters
values. Is there a way to order postgres to check the plan each time the
function is called?

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Julius Tuskenis