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我没想到这会是一项如此艰巨的任务。

用户参加测验，然后出于任何原因决定重新参加测验。

我们的要求是在将结果插入 SurveyAnswers 表之前删除该用户已经完成的测验结果。

下面的代码旨在删除属于尝试重新参加测验的用户的每个 questionId (qid) 的现有结果，然后插入当前结果。

这应该在一个操作中。

然后，如果当前不存在结果，则插入当前测验的结果。

代码没有插入或删除。

非常感谢您的帮助。

这是我的代码：

Private Sub SaveAnswer(ByVal qid As Integer, ByVal cid As Integer, ByVal ct As String, ByVal cscore As Integer)
    Dim al As ArrayList = CType(Session("AnswerList"), ArrayList)

    If al Is Nothing Then
        Response.Redirect("List.aspx")
    End If

    Dim cnn As New SqlConnection(ConfigurationManager.ConnectionStrings("DBConnectionString").ConnectionString)

    Dim cmd As New SqlCommand("IF EXISTS(SELECT QuestionId FROM SurveyAnswers WHERE questionId = @qid and UserName = @cuser " & _
                           "BEGIN delete from SurveyAnswers where UserName=@cuser and QuestionId=@qid " & _
                           "insert into surveyanswers(QuestionID,ChoiceID,ChoiceText,Username,dateTaken) values(@qid,@cid,@ct,@cuser,getDate()) END " & _
                           "Else BEGIN insert into surveyanswers(QuestionID,ChoiceID,ChoiceText,Username,dateTaken) values(@qid,@cid,@ct,@cuser,getDate()) END", cnn)
    Dim p1 As New SqlParameter("@qid", qid)
    Dim p2 As New SqlParameter("@cid", IIf(cid = 0, DBNull.Value, cid))
    Dim p3 As New SqlParameter("@ct", IIf(ct = "", DBNull.Value, ct))
    Dim p4 As New SqlParameter("@cuser", Session("UserName"))
    cmd.Parameters.Add(p1)
    cmd.Parameters.Add(p2)
    cmd.Parameters.Add(p3)
    cmd.Parameters.Add(p4)
    cnn.Open()
    cmd.ExecuteNonQuery()
    cnn.Close()
End Sub
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1 回答 1

0

以下是应 OP 的要求提升为答案的评论：

if exists ( select 42 from SurveyAnswers where ... )
  begin
  delete SurveyAnswers where ...
  end;
insert into SurveyAnswers ...

旁白：请注意，您所做的不是原子的，除非它包含在适当隔离级别的事务中。虽然单个用户不太可能同时多次回答同一个调查问题，但您应该意识到这个问题并做出明确的决定来处理或忽略它。我同意在存储过程中实现它，例如：

create procedure dbo.InsertSurveyAnswer
  -- NB: The prior answer, if any, is deleted.
  @QuestionId as Int,
  @ChoiceId as Int,
  @ChoiceText as NVarChar(64),
  @Username as NVarChar(64)
  as

  set nocount on;

  set transaction isolation level serializable;
  begin transaction;

  -- Attempt to delete any prior answer for this user/question.
  delete from SurveyAnwers
    where Username = @Username and QuestionId = @QuestionId;

  -- Save the new answer.
  insert into SurveyAnswers
    ( QuestionId, ChoiceId, ChoiceText, Username, DateTaken ) values
    ( @QuestionId, @ChoiceId, @ChoiceText, @Username, GetDate() );

  commit transaction;

正如 Martin Smith 所建议的那样，您可能只是简单地执行delete而不是浪费资源来确定是否需要它。如果您有理由知道某行是否被删除，您可以检查@@RowCountafter的值。delete

于 2013-08-18T18:04:05.640 回答