SQL子查询不适用于group by子句

Question

我正在使用SQL Server 2012.任何人都可以告诉我哪里出错了吗？

SELECT 
       avg (tbl.FirstBillComplete) 
      FROM 
       (select l.MONTH, a.OverallScore, (a.FirstBillComplete), (a.EmailComplete) 
        from tbl_T1 a join calls.dbo.c1_LP l on a.QID = l.QID 
         union 
        select l.MONTH, a.OverallScore, (a.FirstBillComplete), (a.EmailComplete) 
        from tbl_2 a join calls.dbo.C3_LP l on a.QID = l.QID 
        union ALL 
        select l.MONTH, a.OverallScore, (a.FirstBillComplete), (a.EmailComplete) 
        from tbl_3 a join c2 l on a.QID = l.QID 
       ) As tbl 
      GROUP BY tbl.MONTH 

我得到的错误是：

No column was specified for column 7 of 'tbl'. 
No column was specified for column 8 of 'tbl' 

Answer 1

您需要为列7和TBL的8指定列名：使用

'' AS MyColumn7, 

例如。