使用別名在SELECT語句中另一列

Question

我希望做我的SELECT查詢和列的一些基本的數學..

SELECT Rider, 
COUNT(if(Result = 1, Result, NULL)) AS "Firsts", 
COUNT(if(Result = 2, Result, NULL)) AS "Seconds", 
COUNT(if(Result = 3, Result, NULL)) AS "Thirds", 
COUNT(if(Result = " ", Result, NULL)) AS "NP", 
COUNT(*) AS "Total", 
"Firsts"/"Total"*100 AS "S/R" 
FROM meeting_master 
WHERE RaceDayDate>="2012-01-01" 
GROUP BY meeting_master.Rider 
ORDER BY Firsts DESC 
LIMIT 100 

我的問題（缺乏的MySQL相關知識）是有S/R列計算在第7行的數學......

Answer 1

你不應該使用別名在SELECT這樣的：

"Firsts"/"Total"*100 AS "S/R" 

而不是直接計算是這樣的：

COUNT(if(Result = 1, Result, NULL))/COUNT(*) * 100 AS "S/R" 

所以您的查詢應該是：

SELECT Rider, 
COUNT(if(Result = 1, Result, NULL)) AS "Firsts", 
COUNT(if(Result = 2, Result, NULL)) AS "Seconds", 
COUNT(if(Result = 3, Result, NULL)) AS "Thirds", 
COUNT(if(Result = " ", Result, NULL)) AS "NP", 
COUNT(*) AS "Total", 
COUNT(if(Result = 1, Result, NULL))/COUNT(*) * 100 AS "S/R" 
FROM meeting_master 
WHERE RaceDayDate>="2012-01-01" 
GROUP BY meeting_master.Rider 
ORDER BY Firsts DESC 
LIMIT 100 

Just see SQLFiddle example here.