Global Ruleset - Global ruleset is applied to all zones. Lacking the entry to the variables table means there is no default ruleset and the rules will use coded defaults.
insert into variables set variable_name='default_ruleset_id',variable_value='1',comment='Default ruleset';
Zone Ruleset - The zones world database table has a parameter ruleset_id which would override the global ruleset for any rules defined under the custom ruleset_id. Any rules not defined in the custom ruleset would default to the global values.