建外建时,指定关系为级联删除(ON DELETE CASCADE)。
例:
CREATE TABLE Emp_tab (
Empno NUMBER(5) CONSTRAINT Emp_pkey PRIMARY KEY,
Ename VARCHAR2(15) NOT NULL,
Job VARCHAR2(10),
Mgr NUMBER(5) CONSTRAINT Mgr_fkey
REFERENCES Emp_tab,
Hiredate DATE,
Sal NUMBER(7,2),
Comm NUMBER(5,2),
Deptno NUMBER(3) NOT NULL
CONSTRAINT dept_fkey REFERENCES Dept_tab ON DELETE CASCADE);
例:
CREATE TABLE Emp_tab (
Empno NUMBER(5) CONSTRAINT Emp_pkey PRIMARY KEY,
Ename VARCHAR2(15) NOT NULL,
Job VARCHAR2(10),
Mgr NUMBER(5) CONSTRAINT Mgr_fkey
REFERENCES Emp_tab,
Hiredate DATE,
Sal NUMBER(7,2),
Comm NUMBER(5,2),
Deptno NUMBER(3) NOT NULL
CONSTRAINT dept_fkey REFERENCES Dept_tab ON DELETE CASCADE);
然后重新建立外键,不过要加上on delete cascade