sql问题 full join问题？SQL unique 键如何删除

select count(*) from (select qybm,xh from a  union select qybm,xh from b) ab group by qybm

删除unique约束吧alter table student drop constraint unique(class) 和 alter table stdent drop constraint class 试一下

details[英][’di:teɪlz] [美][’di:teɪlz]n.详细资料；详述( detail的名词复数 )；（照片、绘画等的）细部；细目；各种细节1.N-COUNT细节The details of something are its individual features or elements. The details of the plan are still being worked out...计划的细节仍在制订中。No details of the discussions have been given...没有透露讨论的细节。I recall every detail of the party.我回想起聚会的每一个细节。2.N-PLURAL详情；信息；资料Details about someone or something are facts or pieces of information about them. See the bottom of this page for details of how to apply for this exciting offer...有关如何申请这一令人兴奋的工作的详情请参见本页底部。Full details will be announced soon.具体信息很快就会公布。3.N-COUNT枝节；末节；琐事A detail is a minor point or aspect of something, as opposed to the central ones. Only minor details now remain to be settled.现在仅剩一些细枝末节的问题需要解决。4.N-UNCOUNT（难以觉察的）细微之处You can refer to the small features of something which are often not noticed as detail .We like his attention to detail and his enthusiasm.我们喜欢他的细心和热情。