CREATE TABLE insured_autos
(policy_id NUMBER CONSTRAINT policy_fk
REFERENCE policies(policy_id
ON DELETE CASCADE,
make VARCHAR2(30),
model VARCHAR(30),
year NUMBER,
CONSTRAIN auto_fk FROEIGN KEY (make,model,year)
REFERENCES automobiles (make,model,year)
ON DELETE SET NULL
);
ON DELETE子串告诉ORACLE如果父纪录(parent record)被删除后,子记录做什么。缺省情况下禁止在子记录还存在的情况下删除父纪录。
(policy_id NUMBER CONSTRAINT policy_fk
REFERENCE policies(policy_id
ON DELETE CASCADE,
make VARCHAR2(30),
model VARCHAR(30),
year NUMBER,
CONSTRAIN auto_fk FROEIGN KEY (make,model,year)
REFERENCES automobiles (make,model,year)
ON DELETE SET NULL
);
ON DELETE子串告诉ORACLE如果父纪录(parent record)被删除后,子记录做什么。缺省情况下禁止在子记录还存在的情况下删除父纪录。
alter table 从表
add constraint a foreign key (CHK_NO)
references 主表(CHK_NO) on delete cascade;以后你要删主表数据,从表也相应的删除。