关于执行效率的问题
测试表a   b
大家谈谈下列两种方式,哪种的执行效率要高些
--1.
select   a.c1,a.c2,sum(a.c3)   as   c3,sum(b.cc)   as   cc
from   a
join   b
on   a.c1=b.c1   and   a.c2=b.c2
where   a.c1 <> 1   and   b.c2 <> 5
group   by   a.c1,a.c2

--2.
select   x.c1,x.c2,x.c3,y.cc
from   (select   c1,c2,sum(c3)   as   c3   from   a   where   a.c1 <> 1   group   by   c1,c2)as   x
join   (select   c1,c2,sum(cc)   as   cc   from   b   where   b.c1 <> 1   group   by   c1,c2)as   y
on   a.c1=b.c1   and   a.c2=b.c2


------解决方案--------------------
用方法1
------解决方案--------------------
建議使用方法一
------解决方案--------------------
方法一的效率高,因为在方法二中运用连接的同时又创建了两个衍生表x和y.