sql - Query compare from a table and a sum of multiple row in another table -

i have question regarding sql query , keep getting error. im trying getting qty value row in master_drawing table , compare same name sum of multiple occurences same key head_mark.

this sql

select master_drawing.total_qty totalqty,         sum(master_drawing_assigned.assigned_qty) sumassignedqty  master_drawing, master_drawing_assigned  head_mark = 'testmultiple' , project_name = 'millhouse' 

what keep getting 'ora-00918: column ambiguously defined'

am doing wrong here? in end, need compare totalqty sumassignedqty further operation

this tabe structure

master_drawing,

  head_mark           varchar2(20 char),   entry_date          date,   comp_type           varchar2(20 char),   weight              number(11,2),   surface             number(15,3),   profile             varchar2(20 char),   project_name        varchar2(20 char),   length              number(15,2)              not null,   total_qty           number(38),   subcont_status      varchar2(20 char),   distribution_count  number 

and master_drawing_assigned,

  assigned_weight    number(12,3),   assigned_qty       number(38),   surface            number(15,3),   subcont_id         varchar2(20 char),   revision_no        number(2),   assignment_date    date,   project_name       varchar2(20 char),   id                 number(3),   head_mark          varchar2(20 char),   assigned_due_date  date,   comp_type          varchar2(25 char),   signature          varchar2(25 char) 

try this:

select md.total_qty totalqty, mda.sumassignedqty  master_drawing md  inner join (select mda.head_mark, mda.project_name, sum(mda.assigned_qty) sumassignedqty              master_drawing_assigned mda              group mda.head_mark, mda.project_name           ) mda on md.head_mark = mda.head_mark , md.project_name = mda.project_name  md.head_mark = 'testmultiple' , md.project_name = 'millhouse';