I have 8 million rows of data from combining these four tables (tbl_user, tbl_missing_child_detail, tbl_recovery_child_detail, tbl_child_profile_details).

In the case that I have the same example data as in this question and additionally declare the following two functions:

I have Postgres SQL function defined like below. It has a part where it runs a select query and has to store it in v_combination_exists variable. But it gives error in select statement.

I have a requirement to dynamically execute a query string. For this I have written a function which generates this query string.