实例：
insert into onethink.ds_ucenter_member (group_id,username,`password`,email,reg_time) select 6 as group_id,d.username,d.`password`,d.email,d.regdate from dsui.pre_ucenter_members as d WHERE not exists (select * from onethink.ds_ucenter_member where onethink.ds_ucenter_member.username = d.username or onethink.ds_ucenter_member.email = d.email );
mysql复制一个表的数据到另一个表,并且指定某个字段的值,两表数据结构可不同
