请教UNION ALL的性能问题
有一这样的视图
select f1,f2,f3,f4,f5 from tab1
union all
select f1,f2,tab2f3 as f3,tab2f4 as f4,tab2f5 as f5 from tab2
union all
select f1,f2,tab3f3 as f3,tab3f4 as f4,tab3f5 as f5 from tab3
union all
select f1,f2,tab4f3 as f3,tab4f4 as f4,tab4f5 as f5 from tab4
union all
select f1,f2,tab5f3 as f3,tab5f4 as f4,tab5f5 as f5 from tab5
where f1='XXXXXX' and f2='xxxxxxxx'
表tab1,2,3,4,5的表结构是不一样的,如果表tab1,2,3,4,5里的数据有每张表有几十万笔数据,查询起来会不会很慢啊?有没有什么优化的办法?