SQL ORA-02256：引用的列數必須與所引用的列

Question

這些都是我的表：

CREATE TABLE EMPLOYEE(
    Emp_id number(4), 
    Emp_name varchar2(30), 
    Emp_gender varchar2(1), 
    Status varchar2(30), 
    Years_service number(4), 
    Primary Key (emp_id) 
); 

CREATE TABLE ACTIVITY(
    Act_id number(4), 
    Description varchar2(30), 
    Category_code varchar2(1), 
    Primary Key(Act_id) 
); 

CREATE TABLE ALLOCATION(
    Emp_id number(4) NOT NULL, 
    Act_id number(4) NOT NULL, 
    Hourly_rate number(5,2) NOT NULL, 
    Primary Key (Act_id, Emp_id), 
    Foreign Key (Act_id) REFERENCES ACTIVITY, 
    Foreign Key (Emp_id) REFERENCES EMPLOYEE, 
    CONSTRAINT CK_ALLOCATION_RATE CHECK(Hourly_rate > 0 and Hourly_rate<300) 
); 

CREATE TABLE ACTION(
    Week_no number(2) NOT NULL, 
    Hrs_worked number(4,1) NOT NULL, 
    Act_id number(4) NOT NULL, 
    emp_id number(4) NOT NULL, 
    Primary Key (Week_no, Act_id, emp_id), 
    Foreign Key (Act_id) References Allocation, 
    Foreign Key (emp_id) References Allocation 
); 

表employee，activity和allocation是完全建立。但是當我嘗試創建表action並將外鍵引用到表allocation時，它說：ORA-02256：引用列的數量必須與引用列匹配。

Answer 1

當使用references我認爲這是一個好主意，包括在都表，即使語法使得這種不必要的（默認是主鍵）列。

你有一個複合主鍵，所以您需要爲外國參考複合鍵：

CREATE TABLE ACTION (
    Week_no number(2) NOT NULL, 
    Hrs_worked number(4,1) NOT NULL, 
    Act_id number(4) NOT NULL, 
    emp_id number(4) NOT NULL, 
    Primary Key (Week_no, Act_id, emp_id), 
    Foreign Key (Act_id, emp_id) References Allocation(Act_id, emp_id) 
);