我的 SQL 代码中的外键有什么问题？

Question

CREATE TABLE Bagel (
  BagelID CHAR(2) NOT NULL,
  BagelName VARCHAR(30),
  BagelPrice DECIMAL(4,2),
  BagelDesc VARCHAR(30),
  PRIMARY KEY (BagelID));
  
CREATE TABLE Customer (
  CustID INT NOT NULL,
  FirstName VARCHAR(30),
  LastName VARCHAR(60),
  Address1 VARCHAR(60),
  Address2 VARCHAR(60),
  City VARCHAR(30),
  State CHAR(2),
  Zip INT,
  MobilePhone VARCHAR(30),
  PRIMARY KEY (CustID));

CREATE TABLE BagelOrder (
  BagelOrderID SMALLINT NOT NULL,
  CustID INT NOT NULL,
  OrderDate DATE, 
  DeliveryFee DECIMAL(4,2),
  SpecNotes VARCHAR(60),
  PRIMARY KEY (BagelOrderID),
  FOREIGN KEY (CustID) REFERENCES Customer(CustID));

CREATE TABLE BagelOrderLineItem (
  BagelOrderID SMALLINT NOT NULL,
  BagelID CHAR(2) NOT NULL,
  BagelQuantity TINYINT,
  PRIMARY KEY (BagelOrderID, BagelID),
  FOREIGN KEY (BagelOrderID) REFERENCES BagelOrder(BagelOrderID)
);

INSERT INTO BagelOrder (BagelOrderID, CustID, OrderDate, DeliveryFee, SpecNotes)
VALUES
  (1, 1, '2023-12-07', 5.99, 'Add Cream Cheese'),
  (2, 2, '2023-12-07', 5.99, NULL),
  (3, 3, '2023-12-14', 6.99, NULL);

INSERT INTO BagelOrderLineItem (BagelOrderID, BagelID, BagelQuantity)
VALUES
  (1, 'RB', 5),
  (2, 'EB', 2),
  (3, 'CB', 1),
  (3, 'NB', 2);
  
INSERT INTO Customer (CustID, FirstName, LastName, Address1, Address2, City, State, Zip, MobilePhone)
  (1, 'Bryn', NULL, '123 ABC Street', NULL, 'Salt Lake City', 'UT', 84101, '8011234567'),
  (2, 'Santa', 'Clause', '1234 S Pole St', NULL, 'Vernal', 'UT', 84078, '8018001234'),
  (3, 'Jane', 'Doe', '1000 W Street', NULL, 'New York City', 'NY', 10000, '8001231234');

INSERT INTO Bagel (BagelID, BagelName, BagelPrice, BagelDesc)
VALUES
  ('RB', 'Radically Raisin Bagel', 2.00, 'Raisin Bagel'),
  ('EB', 'All the Stuff Bagel', 2.35, 'Everything Bagel'),
  ('CB', 'Chip Off the Block Bagel', 2.25, 'Chocolate Chip Bagel'),
  ('MB', "Keepin' It Healthy Bagel", 2.00, 'Multigrain Bagel'),
  ('NB', 'Classic New York Bagel', 1.75, 'New York Bagel');

错误消息显示“无法添加或更新子行：外键约束失败 (

db_9_dc8b6f4

.

bagelorder

, CONSTRAINT

bagelorder_ibfk_1

FOREIGN KEY (

CustID

) REFERENCES

customer

(

CustID

))”

所以我相信我的客户表上的外键有问题，但我不知道它是什么。

Answer 1

如果父表中没有匹配的候选键值，则不能进行任何尝试在子表中创建外键值的 INSERT 或 UPDATE 操作（请参阅 mySQL 文档）。

所以在添加之前

INSERT INTO BagelOrder (BagelOrderID, CustID, OrderDate, DeliveryFee, SpecNotes)
VALUES
  (1, 1, '2023-12-07', 5.99, 'Add Cream Cheese'),
  (2, 2, '2023-12-07', 5.99, NULL),
  (3, 3, '2023-12-14', 6.99, NULL);

您需要有一个匹配的客户ID，但该客户ID不存在，因此您需要在此处更改订单以先添加客户。

INSERT INTO Customer (CustID, FirstName, LastName, Address1, Address2, City, State, Zip, MobilePhone)
  (1, 'Bryn', NULL, '123 ABC Street', NULL, 'Salt Lake City', 'UT', 84101, '8011234567'),
  (2, 'Santa', 'Clause', '1234 S Pole St', NULL, 'Vernal', 'UT', 84078, '8018001234'),
  (3, 'Jane', 'Doe', '1000 W Street', NULL, 'New York City', 'NY', 10000, '8001231234');

INSERT INTO BagelOrder (BagelOrderID, CustID, OrderDate, DeliveryFee, SpecNotes)
VALUES
  (1, 1, '2023-12-07', 5.99, 'Add Cream Cheese'),
  (2, 2, '2023-12-07', 5.99, NULL),
  (3, 3, '2023-12-14', 6.99, NULL);

INSERT INTO BagelOrderLineItem (BagelOrderID, BagelID, BagelQuantity)
VALUES
  (1, 'RB', 5),
  (2, 'EB', 2),
  (3, 'CB', 1),
  (3, 'NB', 2);