Question

我有两个SQL查询。首先，我正在撤回所获得的总分，而在其他方面，我正在返回最大分数。现在我想在单个查询中将两者结合起来，以使其成为单个过程。查询如下：

第一次查询

   select SUM(MarksObtained) as MarksObtained from tbAnswers where QID IN(Select QID from tbQuestions where ExamID =2)

第二次查询

Select SUM(Marks) as MaxMarks from tbQuestions where ExamID =2

我想要下面的内容返回：

Maxmarks | MarksObtained
------------------------
   100        50

我尝试了Union，但它返回了如下内容：

MarksObtained
-------------
100

50

Answer 1

好吧，由于查询不相关，您可以将它们放入select：

SELECT
   (
      select SUM(MarksObtained)  
      from tbAnswers where QID IN (
          Select QID from tbQuestions where ExamID = 2
      )
   ) as MarksObtained,
   (
       Select SUM(Marks)   
       from tbQuestions where ExamID = 2
   ) as MaxMarks

Answer 2

即使有了公认的答案，但有必要提一下，正确的做法是使用单独的查询，因为它们只是在客户端上使用MARS，以防性能成为问题。

更新：这就是你如何组合几个查询并一起阅读它们：

using(var conn = SqlConnection(...)) {
   conn.Open();
   var cmd = conn.CreateCommand()
   cmd.CommandText = 
    @"Select SUM(MarksObtained) as MarksObtained 
      from tbAnswers 
      where QID IN(Select QID from tbQuestions where ExamID =2);"
  + @"Select SUM(Marks) as MaxMarks 
      from tbQuestions 
      where ExamID =2";

   using (var dr = cmd.ExecuteReader) {
        ... // read MarksObtained
        dr.NextResult()
        ... // readMaxMarks
        dr.Close()
   }
   conn.Close()
}

MSDN IDataReader.NextResult

Answer 3

    ;WITH    CTE1 ( MarksObtained )
              AS ( SELECT   SUM(MarksObtained) AS MarksObtained
                   FROM     tbAnswers
                   WHERE    QID IN ( SELECT QID
                                     FROM   tbQuestions
                                     WHERE  ExamID = 2 )
                 ),
            CTE2 ( MaxMarks )
              AS ( SELECT   SUM(Marks) AS MaxMarks
                   FROM     tbQuestions
                   WHERE    ExamID = 2
                 )
        SELECT  MaxMarks,MarksObtained
        FROM    CTE1 ,
                CTE2

将两个不同的不相关SQL查询（返回单列结果）合并为一个包含两列的查询结果

3 个答案: