mysql - Sum records when counter increases -

i displaying records need sum cost sumcost counter increases particular group of records. appreaciate simple sql code. e.g.

group| items | cost   | sumcost| counter ----------------------------------------- cars | opel  | 50     | 50     | 1 cars | toyota| 60     | 110    | 2 cars | kia   | 40     | 150    | 3 laps | acer  | 30     | 30     | 1 laps | hp    | 45     | 75     | 2 laps | compaq| 20     | 95     | 3 , on.... 

want that, e.g. group (cars) displaying records, should sum cost of each car item , display sum/total in sumcost column. sumcost of opel 50, sumcost of toyota (cost of opel , toyota i.e. 50+60=110) , of kia (opel cost + toyota cost + kia cost => 50+60+40=150) etc

here ask, exactly:

select  if(t.counter=1, @sum:=0,null) _, @sum:=@sum+t.cost sum,  t.* t; 

sqlfiddle

sqlfiddle without counter, group changing

i review question , find useful answer
here same solution sum counting:

select *,    (select sum(cost) sometbl counter     t.groups = counter.groups , t.id >= counter.id) cost_sum sometbl t 

fiddle