CREATE TABLE buy_fruits(id int not null auto_increment,primary key(id),fruit_name varchar(30),kg int(11),fruit_id int(11));

CREATE TABLE sold_fruits((id int not null auto_increment,primary key(id),fruit_name varchar(30),sum_kg int(11),fruit_id int(11));

delimiter $$

create trigger insert_test_summ
after insert on buy_fruits
for each row begin
IF buy_fruits.fruit_id=new.fruit_id
THEN
insert into sold_fruits set sum_kg=sold_fruits.sum_kg+  new.kg;
else insert into sold_fruits
set sum_kg=new.kg,fruit_id=new.fruit_id;
end if;
end;