簡單的SELECT查詢導致笛卡爾連接？

我有一個簡單的查詢，我返回4個字段：[Year],[ServiceCredited],[Salary]和[CoveredEmployer]。簡單的SELECT查詢導致笛卡爾連接？

使用Table1，我可以檢索前3個字段，但我無法獲得[CoveredEmployer]。要獲得[CoveredEmployer]，我必須加入到Table2，其中有更多詳細信息，例如Members Employer_Org_ID，然後使用Employer_Org_Id將Table2連接到Table3以獲取僱主名稱或[CoveredEmployer]。

SELECT a.SCHOOL_YEAR as Year, a.TOTAL_SERVICE_CREDIT as ServiceCredited, a.RETIREMENT_SALARY as Salary, c.ORG_NAME as CoveredEmployer 
FROM TBL1 a 
INNER JOIN TBL2 b ON a.MEMBER_ACCOUNT_ID = b.MEMBER_ACCOUNT_ID 
INNER JOIN TBL3 c ON b.ORG_ID = c.ORG_ID 
WHERE a.MEMBER_ACCOUNT_ID = 136079 
ORDER BY YEAR DESC;

我然後，在代碼，由[年]和分組的結果，其中存在多於1名僱主，具有[CoveredEmployer]值是「多僱主」：

var lyosGroupedByYear = lyos.GroupBy(x => x.Year).Select(x => new Years_Of_Service() 
      { 
       Year = x.Key, 
       //ServiceCredited = x.Sum(y => y.ServiceCredited), 
       //Salary = x.Sum(y => y.Salary), 
       ServiceCredited = x.First().ServiceCredited, 
       Salary = x.First().Salary, 
       CoveredEmployer = x.Count() > 1 ? "Multiple Employers" : x.First().CoveredEmployer 
      }).ToList();

的問題我的上面的查詢是，我得到一個Cartesion加入，從而導致產生「多個僱主」的每個記錄，我分組（下面是簡單的2013年的結果，實際結果回到1982年同樣的問題）：

2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Special School Dist-St. Louis 
2014   Hazelwood R-I Schools 
2014   St. Louis Community College 
2014   Special School Dist-St. Louis 
2014   St. Louis Community College 
2014   Special School Dist-St. Louis 
2014   St. Louis Community College 
2014   Special School Dist-St. Louis 
2014   St. Louis Community College 
2014   Special School Dist-St. Louis 
2014   St. Louis Community College 
2014   Special School Dist-St. Louis 
2014   St. Louis Community College 
2014   Special School Dist-St. Louis 
2014   St. Louis Community College 
2014   St. Louis Community College 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Hazelwood R-I Schools 
2013 1 95476.8 St. Louis Community College 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 St. Louis Community College 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 St. Louis Community College 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 St. Louis Community College 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 St. Louis Community College 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 St. Louis Community College 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 St. Louis Community College 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 St. Louis Community College 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis 
2013 1 95476.8 Special School Dist-St. Louis

這是我第一次處理笛卡爾聯接。有沒有人知道在我的查詢中解決這個問題的可能方法？

來源

2014-10-09 Analytic Lunatic

所以，你必須爲每個'tbl1'記錄每個'tbl2'記錄多個'tbl2'記錄，和/或多個'tbl3'記錄？其中一個最終結果的原始數據樣本可能會有所幫助。你爲什麼不在你的查詢中分組/計數？ – 2014-10-09 16:01:04

感謝您的回覆亞歷克斯。我最終弄清楚了這個問題。我有'JOIN'正確的Tbl2＆Tbl3，但是對於Tbl1＆Tbl2，我使用了錯誤的Key值作爲Join。我做了一些其他修改，這是我的問題的來源。 – 2014-10-09 16:30:24

@AnalyticLunatic祝賀你自己解決了你的問題。你能否請你張貼 - 並自己接受 - 你的解決方案，所以這個問題可能會顯示爲「回答」。這對未來的訪客很重要。 – 2014-10-09 17:52:49

原來我加入Tbl1 & Tbl2錯誤的字段。本來應該的MEMBER_CONTR_ID代替MEMBER_ACCOUNT_ID：

SELECT a.SCHOOL_YEAR as Year, a.TOTAL_SERVICE_CREDIT as ServiceCredited, a.RETIREMENT_SALARY as Salary, c.ORG_NAME as CoveredEmployer 
FROM TBL1 a 
INNER JOIN TBL2 b ON a.MEMBER_CONTR_ID = b.MEMBER_CONTR_ID 
INNER JOIN TBL3 c ON b.ORG_ID = c.ORG_ID 
WHERE a.MEMBER_ACCOUNT_ID = 136079 
ORDER BY YEAR DESC;

來源

2014-10-09 21:13:04

簡單的SELECT查詢導致笛卡爾連接？

回答

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