How many users are on list xxx
To determine how many users are subscribed to a particular list, simply query the members_table:
select count(*) from members_ where list_ = 'jazztalk' and MemberType_ = 'normal'
If you want to know the breakdown of members by type, on a list:
select MemberType_, count(*) from members_ where list_ = 'jazztalk' group by MemberType_