Question

任何人都可以请求帮助解决此错误的方法吗？我得到一个错误“错误：查询表达式'''ans'中的语法错误（缺少运算符）。”这是我的代码：

Imports System.Data
Imports System.Data.OleDb
Public Class frmExam : Inherits System.Windows.Forms.Form
 Dim ds As New DataSet()
 Dim qno() As Integer
 Dim pos As Integer

Private Sub btnFinish_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnFinish.Click
    ProcessAnswer()
    Dim i, marks As Integer
    Dim dr As DataRow
    marks = 0
    For i = 0 To NOQ - 1
        dr = ds.Tables(0).Rows(qno(i))
        If Not IsDBNull(dr.Item("ans")) AndAlso dr.Item("CorrectAns") = dr.Item("ans") Then
            marks += 1
        End If
    Next

    Try
        con.Open()
        Dim cmd As New OleDbCommand("insert into stud values(stud.nextval,'" & SubjectCode & "','" & Username & "','" & marks & ")", con)
        MsgBox(cmd.CommandText)
        cmd.ExecuteNonQuery()
        Dim msg As String
        msg = "UserName         : " & Username & ControlChars.CrLf & _
                "Subject        : " & SubjectCode & ControlChars.CrLf & _
                "Total Questions : " & NOQ & ControlChars.CrLf & _
                "Marks           : " & marks
        MsgBox(msg, "Result")
    Catch ex As Exception
        MsgBox(ex.Message)
    Finally
        If con.State <> ConnectionState.Closed Then
            con.Close()
        End If
    End Try
    Me.Dispose()
End Sub

Private Sub frmExam_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    ReDim qno(NOQ)
    Try
        Dim da As New OleDbDataAdapter("select Question, Ans1, Ans2, Ans3, Ans4, CorrectAns, QType, '' ans from question where SubjectCode = " & SubjectCode, con)
        da.Fill(ds, "question")
    Catch ex As Exception
        MsgBox("Error:" & ex.Message)
        Me.Dispose()
    End Try

    Randomize()
    Dim totrows As Integer

    totrows = ds.Tables(0).Rows.Count
    Dim i, r, j As Integer
    Dim present As Boolean
    i = 0
    Do While i < 5
        r = CInt((totrows - 1) * Rnd())
        present = False
        For j = 0 To i
            If r = qno(j) Then
                present = True
                Exit For
            End If
        Next

        If Not present Then
            qno(i) = r
            i = i + 1
        End If
    Loop
    pos = 0
    DisplayQuestion()
End Sub
Sub DisplayQuestion()
    Dim row As DataRow

    lblQno.Text = Str(pos + 1) & "/" & NOQ
    lblSubcode.Text = "Subject : " & SubjectCode
    row = ds.Tables(0).Rows(qno(pos))

    txtQuestion.Text = row.Item(0)
    txtAns1.Text = row.Item(1)
    txtAns2.Text = row.Item(2)
    txtAns3.Text = row.Item(3)
    txtAns4.Text = row.Item(4)

    lblQNo2.Text = Str(pos + 1) & "/" & NOQ
    lblSubCode2.Text = "Subject:" & SubjectCode
    row = ds.Tables(0).Rows(qno(pos))

    txtQuestion2.Text = row.Item(0)
    txtAnsTrue.Text = row.Item(1)
    txtAnsFalse.Text = row.Item(2)

    lblQNo3.Text = Str(pos + 1) & "/" & NOQ
    lblSubcode.Text = "Subject : " & SubjectCode
    row = ds.Tables(0).Rows(qno(pos))

    txtQuestion3.Text = row.Item(1)
    txtAns.Text = row.Item(2)


    End Sub

Private Sub btnNext_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnNext.Click
    ProcessAnswer()
    If pos < NOQ - 1 Then
        pos = pos + 1
        DisplayQuestion()
    Else
        Beep()
    End If
End Sub

Private Sub btnPrev_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPrev.Click
    ProcessAnswer()
    If pos > 0 Then
        pos = pos - 1
        DisplayQuestion()
    End If
End Sub
Public Sub ProcessAnswer()
    Dim row As DataRow
    Dim ans As String = ""
    row = ds.Tables(0).Rows(qno(pos))
    If rdbtnAns1.Checked Then
        ans = "1"
    End If
    If rdbtnAns2.Checked Then
        ans = "2"
    End If
    If rdbtnAns3.Checked Then
        ans = "3"
    End If
    If rdbtnAns4.Checked Then
        ans = "4"
    End If

    If rdbtnTrue.Checked Then
        ans = "1"
    End If
    If rdbtnFalse.Checked Then
        ans = "2"
    End If

    If txtAns.Text = "" Then
        ans = "txtAns"
    End If
    ds.Tables(0).Rows(qno(pos)).Item("Ans1") = ans
End Sub

Private Sub btnPrev2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPrev2.Click
    ProcessAnswer()
    If pos > 0 Then
        pos = pos - 1
        DisplayQuestion()
    End If
End Sub

Private Sub btnNext2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnNext2.Click
    ProcessAnswer()
    If pos < NOQ - 1 Then
        pos = pos + 1
        DisplayQuestion()
    Else
        Beep()
    End If
End Sub

Private Sub btnPrev3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPrev3.Click
    ProcessAnswer()
    If pos > 0 Then
        pos = pos - 1
        DisplayQuestion()
    End If
End Sub

Private Sub btnNext3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnNext3.Click
    ProcessAnswer()
    If pos < NOQ - 1 Then
        pos = pos + 1
        DisplayQuestion()
    Else
        Beep()
    End If
End Sub
End Class

这是突出显示的texxt：totrows = ds.Tables（0）.Rows.Count

Answer 1

如果要为字段表达式使用别名，Access要求您使用AS关键字。

这会失败......

select Question, Ans1, Ans2, Ans3, Ans4, CorrectAns, QType, '' ans from question

可以工作......

select Question, Ans1, Ans2, Ans3, Ans4, CorrectAns, QType, '' AS ans from question

但是，对于名称与表名匹配的字段，我会感到不安。如果您无法重命名该字段，请对表进行别名，并使用表别名限定字段。

select q.Question, q.Ans1, q.Ans2, q.Ans3, q.Ans4, q.CorrectAns, q.QType, '' AS ans from question AS q

IndexOutOfRangeException未处理。找不到表0

1 个答案: