SQL case when和IIF的使用實例

SQL case when的使用實例

數據表：CaseWhen

ID	website1	website2	website3	Name
1	null	www.mozhenlong.com	www.mozhenlong.xin	mzl
2	www.baidu.com	www.mozhenlong.com	null	mzl1
3	null	null	www.mozhenlong.xin	mzl
4	null	www.mozhenlong.com	null	mzl1
5	www.baidu.com	null	www.mozhenlong.xin	mzl
6	null	www.mozhenlong.com	null	mzl1
7	null	www.mozhenlong.com	www.mozhenlong.xin	mzl
8	null	www.mozhenlong.com	null	mzl1
9	www.baidu.com	www.mozhenlong.com	nill	mzl
10	null	null	www.mozhenlong.xin	mzl2
11	null	www.mozhenlong.com	null	mzl
12	www.baidu.com	www.mozhenlong.com	null	mzl2
13	null	null	www.mozhenlong.xin	mzl2
14	null	null	www.mozhenlong.xin	mzl3

統計每個用戶訪問各個站點的總數：

使用case when查詢語句：

 select Name,
 SUM(case website1 when 'www.baidu.com' then 1 else 0 end) as BaiduPost,
 SUM(case website2 when 'www.mozhenlong.com' then 1 else 0 end) as MzlComPost,
 SUM(case website3 when 'www.mozhenlong.xin' then 1 else 0 end) as MzlXinPost 
 from CaseWhen
 group by Name
 order by Name

使用IIF查詢語句：

 select Name,
 SUM(IIF(website1 = 'www.baidu.com',1,0) as BaiduPost,
 SUM(IIF(website2 = 'www.mozhenlong.com',1,0) as MzlComPost,
 SUM(IIF(website3 = 'www.mozhenlong.xin',1,0) as MzlXinPost 
 from CaseWhen
 group by Name
 order by Name

統計結果：

Name	BaiduPost	MzlComPost	MzlXinPost
mzl	2	4	4
mzl1	1	4	0
mzl2	1	1	2
mzl3	0	1	1