SQL & PL/SQL :: Include / Exclude In One Query Statement

how to write this query using all three tables in one query statement.

Result:

Input value of "GM" would return "GM@EMAIL.COM"

Input value of "GM" and "GMC" would return "GMC@EMAIL.COM"

If "GM" is supplied, then only return the "GM@EMAIL.COM" email.

If "GM" and "GMC" is supplied, then only return the "GMC@EMAIL.COM" email

Test Case : GM would return "GM@EMAIL.COM" email

Test Case : GM and GMC would return "GMC@EMAIL.COM" email

select email
from email a,
company b,
sub_company c
where (company = "GM" but no match found in sub_company)
(company = "GM" and sub_company_name = "GMC" match is found in sub_company)

[code]....