修改表时添加约束
alter table userinfo f4
add constraint fk typeid alter foreign key(typeid new)references typeinfo(typeid);


create table userinfo_f4
(id varchar2(10) primary key,
username varchar2(20),
typeid_new varchar2(10));
alter table userinfo_f4
add constraint fk_typeid_alter foreign key(typeid_new)references typeinfo(typeid);
FOREIGN KEY

--在修改表时添加外键约束
ADD CONSTRAINT constraint_name FOREIGN KEY (column_name) REFERENCES
table_name (column_name)[ON DELETE CASCADE]
--constraint_name 外键名
--table_name 主表
--创建一个表
CREATE TABLE xcx_userinfo(
id varchar2(10) primary key,
username varchar2(20),
typeid_new varchar2(10)
);
--添加外键
alter table xcx_userinfo ADD CONSTRAINT pk_typid_alter FOREIGN KEY (typeid_new)
REFERENCES typeinnfo(typeid);
在修改表时添加外键约束:
Alter Table table_name Add Constraint constraint_name Foreign Key(column_name) References table_name(column_name) [On Delete Cascade];
在修改表时添加外键约束
ADD CONSTRAINT containt_name FOREIGN KEY(column_name) REFERENCS table_name(column_name) [ON DELETE CASCADE]
例:
创建一个表
create table userinfo_f4
(
id varchar2(10) primary key,
username varchar2(20),
typeid_new varchar2(10)
);
// 修改时 添加外键约束
alter table userinfo_f4 add constraint fk_typeid_alter foreign key (typeid_new) references typeinfo(typeid) on delete cascade;
修改表时设置外键约束实例
修改表是添加外键约束语法
在修改表时添加外键约束
ADD CONSTRAINT constraint_name FOREIGN KEY(column_name) REFERENCES table_name(column_name)[ON DELETE CASCADE];
------------------------------------------
create table userinfo_f4
(id varchar2(10) primary key,
username varchar2(20),
typeid_new varchar2(10));
-------------------------------------
alter table userinfo_f4
add constraint fk_typeid_alter foreign key(typeid_new) reference typeinfo(typeid);
修改表时添加外键约束
语法:如图,该语句也是放置在ALTER TABLE 表名后面。

举例:此时用户表的用户编号字段是没有设置外键的,通过修改来设置外键。

修改表时添加外键约束
语法:如图,该语句也是放置在ALTER TABLE 表名后面。

举例:此时用户表的用户编号字段是没有设置外键的,通过修改来设置外键。

alter table userinfo_f4
add constraint fk_typeid_alter foreign key(typeid_new) references typeinfo(typeid) 修改表时添加主键约束
在修过表时添加外键约束
ADD CONSTRAINT constraint_name FOREIGN KEY(column_name) REFERENCES table_name(column_name)[ON DELETE CASCADE]
在修改表的时候添加外检约束:
在修改表时添加外键约束
add constraint fk_typeid_alter foreign key(typeid_new)references typeinfi(typeid);
alter table userinfo_f4 add constraint fk_typeid_alter foreign key(typeid_new) reference typeinfo(typeid);
在修改表时添加外键约束:
ALTER TABLE table_name ADD CONSTRAINT constraint_name FOREIGE KEY(column_name) REFERENCES table1(column_name)[ON DELETE CASCADE];
alter table userinfo_f4
add constraint fk_typeid foreign key(typeid_new) references typeinfo(typeid) on delete cascade;
修改表时添加外键约束
alter table table_name
add constraint constraint_name foreign key(column_name) references
table_name(column_name) [on delete cascade]
修改表的时候添加主键约束:
alter table [table_name]
add constraint constraint_name(不能重复) foreign key(table_column) references 主表名(主表主键);
alter table table_name
add constraint constraint_name foreign key ( column_name)
references table_name1(column_name1);