Using Loops in one Table through other Table

Question

There are two Tables A & B.

Table A:

Table B

Now, the conventional and the messy SQL to get the desired output looks as follows:

select person, discount from a where Age >18 and category = 'Gold'
union all
select person, discount from a Age = 18 and category = 'General'

Table A includes multiple other characteristics/measures for person and is of 1 Million in rows.

Table B contains multiple rules for the discount calculation.

Currently, I am solving this through manually using the union all statement.

Please advice if any PL/SQL or stored proc may be using over Amazon Redshift to resolve the same.