简单的SELECT查询导致笛卡尔连接？

我有一个简单的查询，我返回4个字段：[Year],[ServiceCredited],[Salary]和[CoveredEmployer]。简单的SELECT查询导致笛卡尔连接？

使用Table1，我可以检索前3个字段，但我无法获得[CoveredEmployer]。要获得[CoveredEmployer]，我必须加入到Table2，其中有更多详细信息，例如Members Employer_Org_ID，然后使用Employer_Org_Id将Table2连接到Table3以获取雇主名称或[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;

我然后，在代码，由[年]和分组的结果，其中存在多于1名雇主，具有[CoveredEmployer]值是“多雇主”：

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();

的问题我的上面的查询是，我得到一个Cartesion加入，从而导致产生“多个雇主”的每个记录，我分组（下面是简单的2013年的结果，实际结果回到1982年同样的问题）：

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

这是我第一次处理笛卡尔联接。有没有人知道在我的查询中解决这个问题的可能方法？

来源

2014-10-09 Analytic Lunatic

所以，你必须为每个'tbl1'记录每个'tbl2'记录多个'tbl2'记录，和/或多个'tbl3'记录？其中一个最终结果的原始数据样本可能会有所帮助。你为什么不在你的查询中分组/计数？ – 2014-10-09 16:01:04

感谢您的回复亚历克斯。我最终弄清楚了这个问题。我有'JOIN'正确的Tbl2＆Tbl3，但是对于Tbl1＆Tbl2，我使用了错误的Key值作为Join。我做了一些其他修改，这是我的问题的来源。 – 2014-10-09 16:30:24

@AnalyticLunatic祝贺你自己解决了你的问题。你能否请你张贴 - 并自己接受 - 你的解决方案，所以这个问题可能会显示为“回答”。这对未来的访客很重要。 – 2014-10-09 17:52:49

原来我加入Tbl1 & Tbl2错误的字段。本来应该的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;

来源

2014-10-09 21:13:04

简单的SELECT查询导致笛卡尔连接？

回答

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