Query Tunning related to function

[Kumar, Mukesh]

Hi Team,

We are running the below query in PostgreSQL and its taking approx. 8 to 9 sec 
to run the query.

Query - 1

Select * from
  (
  Select payment_sid_c,
  lms_app.translate_payment_status(payment_sid_c) AS paymentstatus
  from
  lms_app.lms_payment_check_request
  group by payment_sid_c) a
  where  paymentstatus in ('PAID', 'MANUALLYPAID')


The explain plan and other details are placed at below link for more 
information. We have checked the indexes on column but in the explain plan it 
is showing as Seq Scan which we have to find out.


https://explain.depesz.com/s/Jsiw#stats


This query is using a function translate_payment_status on column payment_sid_c 
whose script is attached in this mail

Could please anyone help or suggest how to improve the query performance.

Thanks and Regards,
Mukesh Kumar

function.sql
Description: function.sql