查找数据库的不同元素

求教：查找数据库的不同元素
将两个不同数据库的两张不同表的字段值做对比，如果相同则不显示，否则显示出来

例如数据库A的表t1的某字段有值1,2,4,5，数据库B的表t2的某字段有值1,2,3,4,5,6,7,8,9,10，处理后的结果应该显示3,6,7,8,9,10，请问该如何实现？

[解决办法]
select id, 'a' as memo from a where id not in (select id from b)
union all
select id, 'b' from b where id not in (select id from a)
[解决办法]
select t1, 'a表' as memo from a where t1 not in (select t1 from b)
union all
select t2 as t1 , 'b表' as memo from b where t2 not in (select t1 from a)