Dynamic WHERE clause to call DB-function

I was wondering if something like this could be possible:

SELECT * FROM table1
WHERE a1 = ... AND a2 = ... AND b1 = ... AND b2 = ...

The first thing to note is that the WHERE clause is dynamic, as in it can
contain more parameters or lesser parameters.

But, what I want to try accomplish is that this query will return a type
B{b1,b2,...,}.

This type is pre-defined for each defined “table1”.

So the part where we have "b1 = ... AND b2 = ...”, this will apply like a
normal query-selection criteria over the returned results.

But what’s the main thing here is that the first part "a1 = ... AND a2 =
...” (i.e. anything this is not defined in B-type), I want to pass into a
function as a name/value pairs, for example func1(a1=...,a2=...), or maybe
even just a concatenation of String. It is also know that any defined func1
will always return a certain type, say B.

At the end of the day: I like the user to feel they're querying a table, but
in fact, for certain WHERE-clause params they are invoking a function, and
for others, it is applying a selection over the results returned.

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