I am using query explain to show what happens when extra indexes are created
to cover queries

http://dev.mysql.com/doc/refman/5.0/en/query-speed.html

http://dev.mysql.com/doc/refman/5.0/en/select-speed.html

mysql5 -u root people

describe residences;
show index from residences;

join through this table needs to hit index and data table

check statistics / query distribution
http://dev.mysql.com/doc/refman/5.0/en/select-speed.html ( myisamchk )


explain extended select p.name,a.city,a.state from people p left join residences on p.id = person_id left join addresses a on address_id = a.id where p.id=55;


explain  extended
 select  p.name,a.city,a.state
   from  people p
   join  residences on p.id = person_id
   join  addresses a on address_id = a.id
   where p.id=55;