MySQL foreign key causing table to drop

问题

had an issue before with this code which was resolved and caused the table to work but now i am receiving error 1005 and the table cannot be created due to the fk

here is the code for the first table

SET FOREIGN_KEY_CHECKS = 0;
DROP TABLE IF EXISTS Customer;
CREATE TABLE Customer
(
CustomerNumber int NOT NULL,
CustomerName varchar(255),
CustomerAddress varchar(255),
CustomerPhoneNumber varchar(255),
JoinDate varchar(255),
PetName varchar(255),
PayScheme varchar(255),
PremiumPayDate varchar(255),
PRIMARY KEY (CustomerNumber)
);

and here is the code for the second table

DROP TABLE IF EXISTS Policies;    
CREATE TABLE Policies
(
PolicyID int NOT NULL,
PolicyNumber int NOT NULL,
PetType varchar(255),
CustomerNumber int NOT NULL, 
PetName varchar(255),
EffectiveDate varchar(255),
PRIMARY KEY (PolicyID),
    CONSTRAINT fk_CustomerNumber
    FOREIGN KEY (CustomerNumber)
    REFERENCES Customer(CustomerNumber),
    CONSTRAINT fk_PetName
    FOREIGN KEY (PetName)
    REFERENCES Customer(PetName)
    );

error code is

      19:05:38CREATE TABLE Policies (     PolicyID int NOT NULL,     PolicyNumber int NOT NULL,     PetType varchar(255),     CustomerNumber int NOT NULL,      PetName varchar(255),     EffectiveDate varchar(255),     PRIMARY KEY (PolicyID),         CONSTRAINT fk_CustomerNumber FOREIGN KEY (CustomerNumber) REFERENCES Customer(CustomerNumber),  CONSTRAINT fk_PetName     FOREIGN KEY (PetName)     REFERENCES Customer(PetName) )    Error Code: 1005. Can't create table 'cis22723684.Policies' (errno: 150)    0.031 sec

i have resolved the issue see code edited.

  SET FOREIGN_KEY_CHECKS = 0;
  DROP TABLE IF EXISTS Customer;
  CREATE TABLE Customer
  (
     CustomerNumber int NOT NULL,
     CustomerName varchar(255),
     CustomerAddress varchar(255),
     CustomerPhoneNumber varchar(255),
     JoinDate varchar(255),
     PetName varchar(255),
     PayScheme varchar(255),
     PremiumPayDate varchar(255),
     PRIMARY KEY (CustomerNumber, PetName)
     );

     DROP TABLE IF EXISTS Policies;    
     CREATE TABLE Policies
     (
     PolicyID int NOT NULL,
     PolicyNumber int NOT NULL,
     PetType varchar(255),
     CustomerNumber int NOT NULL, 
     PetName varchar(255),
     EffectiveDate varchar(255),
     PRIMARY KEY (PolicyID),
     CONSTRAINT fk_CustomerNumber
     FOREIGN KEY (CustomerNumber, PetName)
     REFERENCES Customer(CustomerNumber, PetName)
     );

it appeared to be using the pk as composite and including the pks under one constraint

however when i attempt to create a new fk i am receiving the same error code as before despite keeping the code used

first table

  SET FOREIGN_KEY_CHECKS = 0;
  DROP TABLE IF EXISTS Customer;
  CREATE TABLE Customer
  (
    CustomerNumber int NOT NULL,
    CustomerName varchar(255),
    CustomerAddress varchar(255),
    CustomerPhoneNumber varchar(255),
    JoinDate varchar(255),
    PetName varchar(255),
    PayScheme varchar(255),
    PremiumPayDate varchar(255),
    PRIMARY KEY (CustomerNumber, PetName)
    );

second table

  DROP TABLE IF EXISTS Policies;    
  CREATE TABLE Policies
  (
   PolicyID int NOT NULL,
   PolicyNumber int NOT NULL,
   PetType varchar(255),
   CustomerNumber int NOT NULL, 
   PetName varchar(255),
   EffectiveDate varchar(255),
   PRIMARY KEY (PolicyID), 
      CONSTRAINT fk_CustomerNumber_PetName
      FOREIGN KEY (CustomerNumber, PetName)
      REFERENCES Customer(CustomerNumber, PetName)
   );

third table

  DROP TABLE IF EXISTS Claims;    
  CREATE TABLE Claims
  (
   ClaimsID int NOT NULL,
   AmountForReimbursement varchar(255),
   PolicyID varchar(255),
       PRIMARY KEY (ClaimsID),
       CONSTRAINT fk_PolicyID
       FOREIGN KEY (PolicyID)
       REFERENCES Policies(PolicyID)      
   );

was a simple matter of the int NOT NULL being identified as varchar, i need some sleep :')

回答1:

Problem is in the second constraint as below where you are trying to reference a non-key column PetName which is not possible and it's against normalization concept. Your Customer table defines only primary key as PRIMARY KEY (CustomerNumber).

CONSTRAINT fk_PetName
FOREIGN KEY (PetName)
REFERENCES Customer(PetName)

Remove the above mentioned FK constraint definition from your CREATE statement and it works just fine. Don't believe then see this fiddle: http://sqlfiddle.com/#!9/86a927

Per your edit: Your FK constraint definition has to be like below. See the modified fiddle: http://sqlfiddle.com/#!9/3a019

CONSTRAINT fk_CustomerNumber_PetName
FOREIGN KEY (CustomerNumber, PetName)
REFERENCES Customer(CustomerNumber, PetName)

来源：https://stackoverflow.com/questions/41492501/mysql-foreign-key-causing-table-to-drop