Check out example codes for "postgres if else". It will help you in understanding the concepts better.

Code Example 1

DO $$
DECLARE
  a integer := 10;
  b integer := 20;
BEGIN 
  IF a > b THEN
	RAISE NOTICE 'a is greater than b';
  END IF;

  IF a < b THEN
	RAISE NOTICE 'a is less than b';
  END IF;

  IF a = b THEN
	RAISE NOTICE 'a is equal to b';
  END IF;
END $$;

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