有4张表做如下关联查询,其中c表有100多万条记录,请问如何做查询优化,让查询速度更快些
select b.mc from a,b where a.id=b.id union all
select c.mc from c,d where c.id=d.id
select b.mc from a,b where a.id=b.id union all
select c.mc from c,d where c.id=d.id
create unique clustered index index_name on tablename(columnname)