variable variables for tablename

Try:

$i = "_id";
$used_table[$i] = $rowcheck->$used_table[$i];

Do this:
$used_table = "search";
$used_table_id = $used_table."_id";
$$used_table_id = $rowcheck->$used_table_id;

That will create the same result as:
$search_id = $rowcheck->search_id;

You might also consider using the extract() function.

Please show us the $rowcheck object.  I smell something fishy in this design pattern and I think if we knew a little more about what you're working toward we could suggest a design pattern that would be more secure and less brittle than what I sense may be going on here.

Yes, I should use another design pattern.
But this example works the best

Thanks