错误 1005 (HY000) mySql，在小型数据库上

Question

嘿，所以我刚开始使用 mysql 并制作了一个小型数据库，但后来我试图改变一些 tables 来实现一些外键，但我得到了错误：ERROR 1005 (HY000 ): 无法创建 table etron3.purchase (errno: 150 "Foreign key constraint is incorrectly formed").

我知道将 TillNo 更改为 TillN 的外键时的原因，但我真的看不出问题是什么。

create table BRANCH(BranchNo INT, BranchAddr VARCHAR(25), BranchTell INT, PRIMARY KEY(BranchNo));


/*Create table CUSTOMER*/
create table CUSTOMER(CustNum INT, CustTell INT, CustFname VARCHAR(15), CustLname VARCHAR(15), CustCountry VARCHAR(20),
CustTown VARCHAR(20), CustStreet VARCHAR(20), CustPostCode CHAR(7), CustDob DATE, CustEmail VARCHAR(45), PRIMARY KEY(CustNum, CustTell));


/*Create table ASSISTANT*/
create table ASSISTANT(SalesPNo INT,TillN INT , SalePFname VARCHAR(20), SalePLname VARCHAR(20), PRIMARY KEY(SalesPNo, TillN));


/*Create table PURCHASE*/
create table PURCHASE(TDateTime DATETIME, TillNo INT, CustNo INT, AssistantNo INT, ProdCode INT, Qty INT, PRIMARY KEY(TDateTime));


/*Create table SUPPLIER*/
create table SUPPLIER(SupCnum INT, SupCname VARCHAR(15), SupFname VARCHAR(15), SupLname VARCHAR(15), SupEmail VARCHAR(30), ProdNum INT, PRIMARY KEY(SupCnum));


/*Create table PRODUCT*/
create table PRODUCT(ProductCode INT, PType VARCHAR(20), Price INT, OfferPrice INT, PRIMARY KEY(ProductCode, PType));


/*Create table PRODTYPE*/
create table PRODTYPE(ProdGroup VARCHAR(20), PCode INT, PRIMARY KEY(ProdGroup));



/*Altering tables, adding foreign keys, so that I don't get any errors*/



/*Add primary and foreign keys to PURCHASE*/

ALTER TABLE PURCHASE
ADD FOREIGN KEY(AssistantNo) REFERENCES ASSISTANT(SalesPNo);

ALTER TABLE PURCHASE
ADD FOREIGN KEY(ProdCode) REFERENCES PRODUCT(ProductCode);

ALTER TABLE PURCHASE
ADD FOREIGN KEY(CustNo) REFERENCES CUSTOMER(CustNum);

ALTER TABLE PURCHASE
ADD FOREIGN KEY (TillNo) REFERENCES ASSISTANT(TillN);

/*Add foreign key to SUPPLIER*/
ALTER TABLE SUPPLIER
ADD FOREIGN KEY(ProdNum) REFERENCES PRODUCT (ProductCode);


/*Add primary and foreign keys to PRODTYPE*/

ALTER TABLE PRODTYPE
ADD FOREIGN KEY(PCode) REFERENCES PRODUCT(ProductCode);

Answer 1

考虑这部分代码：

ALTER TABLE PURCHASE
ADD FOREIGN KEY(AssistantNo) REFERENCES ASSISTANT(SalesPNo);

ALTER TABLE PURCHASE
ADD FOREIGN KEY (TillNo) REFERENCES ASSISTANT(TillN);

ASSISTANT table 的主键是 (SalesPNo, TillN)。

从技术上讲，您不能仅在另一个 table 的主键的第二列有一个外键点 - MySQL 希望对引用的列进行索引，或者显示 复合索引中的第一个。

功能上，您很可能想要一个复合外键而不是两个单独的外键，因此：

ALTER TABLE PURCHASE
ADD FOREIGN KEY (AssistantNo, TillNo) REFERENCES ASSISTANT(SalesPNo, TillN);

通过此更改，您的脚本在 this db fiddle 中成功运行。

推荐阅读：MySQL Foreign Keys - Constraints and Restrictions.

错误 1005 (HY000) mySql，在小型数据库上

ERROR 1005 (HY000) mySql, on small database

mysql

sql

database

foreign-keys

create-table