In Ansible, how to get a variable from another variable and then fetch it's value

Here is my problem I need to use one variable ‘RDS_SG_NAME’ and then append ‘_id’ to it’s value to get another variable name which value I want/need. My simple playbook look like this:

---
- hosts: localhost
  connection: local
  gather_facts: no 
  vars:
    abc_id: 'some-value'
    RDS_SG_NAME: 'abc'
    RDS_SG_ID: "{{ RDS_SG_NAME +'_id' }}"
  tasks:
    - debub: msg="{{ RDS_SG_NAME }}"
    - debub: msg="{{ RDS_SG_ID }}"

when I run this playbook, it give the values like this: RDS_SG_NAME: abc RDS_SG_ID: abc_id But I want the some-value againt it, can someone point me to the right direction.

Thanks in advance

I do this generally, if I want to use a variable name as a value to another variable

Ignore pre_tasks in second play.
The thing to note is the usage of hostvars.