SQL多个外键指向同一主键

Question

Is there going to be a problem with my following design? Basically, I want keep track of a total payment by a customer (eg. $50) that is split between two items (eg. $20 and $30). But I want to be able to look at any item - ITEM(ITEM_ID) and know how much the customer spent on their total bill - PAYMENT(PAYMENT_AMOUNT). To keep it simple I included minimal columns:

CREATE TABLE ITEM (
  ITEM_ID           NUMBER(7,0)         NOT NULL,
  ITEM_SALE_AMT     NUMBER(7,2)         NOT NULL,
  PAYMENT_ID        NUMBER(7,0)         NOT NULL,
  PRIMARY KEY (ITEM_ID),
  FOREIGN KEY (PAYMENT_ID) REFERENCES PAYMENT(PAYMENT_ID)
);

CREATE TABLE PAYMENT (
  PAYMENT_ID        NUMBER(7,0)         NOT NULL,
  PAYMENT_AMOUNT    NUMBER(7,2)         NOT NULL,
  ITEM_1            NUMBER(7,0)         ,
  ITEM_2            NUMBER(7,0)         ,
  PRIMARY KEY (PAYMENT_ID),
  FOREIGN KEY (ITEM_1) REFERENCES ITEM(ITEM_ID),
  FOREIGN KEY (ITEM_2) REFERENCES ITEM(ITEM_ID)
);

Firstly, each item is unique (so you can't have two payments for the same item). Obviously, if the customer pays for many items in one transaction, my PAYMENT table will have a lot of columns (but this has never happened in 30 years, usually 1 and occasionally 2 or 3).

Is there a major flaw I am not seeing or could this be improved?

Answer 1

This is a simple one-to-many relationship. You should take out the ITEM_1 and ITEM_2 columns and associated foreign keys in the PAYMENT table. The items are all linked to their payments via the foreign key in the ITEM table. That's all you need.