关于一个字段同时关联了两个主键
我想做的是表t的字段做为外键，通过关联表1的主键1，表2的主键2。此时只要主键1或主键2中有值，那么就允许表t插入相应的记录。下面的对应的详细的描述：
例如有这样的两张表：
create table a(UserNumber varchar(20) ,primary key (UserNumber)
constraint PK_ID1);
create table b(GroupNumber varchar(20) ,primary key (GroupNumber)
constraint PK_ID2);
分别把table a中的UserNumber ，table b中的GroupNumber建成主键。
此时一张表t，
create table t(userNumber varchar(20));
table t中的usernumber分别做为table a以及table b的外键。如：
alter table t
add constraint foreign key (UserNumber)
references a (UserNumber) on delete cascade
constraint FK_ID1;
alter table t
add constraint foreign key (UserNumber)
references b (GroupNumber) on delete cascade
constraint FK_ID2;
然后先在table a以及table b中insert两条记录：
insert into a values('a1');
insert into b values('b1');
此时往table t中insert 时出错：
insert into t values('a1');
-691 Missing key in referenced table for referential constraint
constraint-name.
A referential constraint has been violated. This condition usually
occurs when you are trying to insert a value into or update the value
of a column that is part of a referential constraint. The value you are
trying to enter does not exist in the referenced (parent-key)
column. If you are using cascading deletes, database logging must be
on.
自己顶一个
求助版主，帮忙分析一下
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