合并sql数据

create table BILL
(
  BILL_ID NUMBER not null,   --主键
  CHARGE  NUMBER,            --钱
  PAY_ID  NUMBER             --外键，关联PAYMENT表的PAY_ID字段
)

insert into bill(bill_id,charge,pay_id) values(1,10,1);
insert into bill(bill_id,charge,pay_id) values(2,10,1);
insert into bill(bill_id,charge,pay_id) values(3,30,2);
insert into bill(bill_id,charge,pay_id) values(4,40,2);



create table PAYMENT
(
  PAY_ID NUMBER not null,    --主键（主表）
  CHARGE NUMBER              --钱
)


insert into payment(pay_id,charge) values (1,0);
insert into payment(pay_id,charge) values (2,0);

合并后：
payment表数据：
pay_id    charge
1          20
2          70

MERGE INTO payment T1
USING (select pay_id, sum(charge) as charge from bill group by pay_id) T2
ON (T1.pay_id = T2.pay_id)
WHEN MATCHED THEN
  UPDATE SET T1.charge = T2.charge
WHEN NOT MATCHED THEN
  INSERT (pay_id, charge) VALUES (T2.pay_id, T2.charge);