foreach row (id,hid,instance,etc...) in table1
   lookup row in table2 that contains id,hid
   lookup a row in table3 that contains id,hid,instance

##</code><code>##

 load all of table2 into a hash, keyed by "id,hid"
 load all of table3 into a hash, keyed by "id,hid,instance"

 foreach row (id,hid,instance,etc...) in table1
   do something with row data, $table2{"id,hid"} and $table3{"id,hid,instance"}