二维离散型随机变量的相关性系数？

Question

公式链接如下：
http://image.baidu.com/i?ct=503316480&z=&tn=baiduimagedetail&word=%CF%E0%B9%D8%CF%B5%CA%FD&in=10197&cl=2&lm=-1&st=&pn=36&rn=1&di=364710842150&ln=1868&fr=&fm=&fmq=1336045717119_R&ic=&s=&se=&sme=0&tab=&width=&height=&face=&is=&istype=#pn36&-1&di364710842150&objURLhttp%3A%2F%2Fwww.gk300.com%2Fasad%2FUploadFiles_3632%2F201101%2F2011011815144420.jpg&fromURLhttp%3A%2F%2Fwww.gk300.com%2Fasad%2Fcxbnx%2Fklyfd%2F378644.shtml&W277&H100&T8639&S8&TPjpgSQL中有哪些简洁的办法解决？

Answer 1

作为新手，先发一个自己写的吧drop table #tbcreate table #tb(x float null,y float null)
insert into #tb values
(1,2.4),
(3.2,5),
(2,4),
(4.4,9.3),
(3.2,null),
(null,null),
(6,3);
go
--select * from #tbselect sum((x-avgx)*(y-avgy))*1.0/power(sum(power(x-avgx,2))*sum(power(y-avgy,2)),0.5) 
from
(select x,y from #tb)t1
cross join
(select avg(x) avgx,avg(y) avgy from #tb)t2