Question

我有一个代码来确定数据是否已经存在。问题是，它甚至还在添加，甚至已经存在。

已经尝试了一些将添加或不添加数据的代码

If txtHostname.Text = "" Then
            MsgBox("Please fill-up all fields!", MsgBoxStyle.Exclamation, "Inventory!")
        Else
            Dim theQuery As String = "SELECT * FROM Asset WHERE Monitor1=@Monitor1 AND Monitor2=@Monitor2"
            Dim cmd1 As OleDbCommand = New OleDbCommand(theQuery, con)
            cmd1.Parameters.AddWithValue("@Monitor1", txtMonitor1.Text)
            cmd1.Parameters.AddWithValue("@Monitor2", txtMonitor2.Text)

            Using reader As OleDbDataReader = cmd1.ExecuteReader()
                If reader.HasRows Then
                    ' User already exists
                    MsgBox("User Already Exist!", MsgBoxStyle.Exclamation, "Add New User!")
                Else
                    ' User does not exist, add them
                    Dim cmd As OleDbCommand = New OleDbCommand("Insert into Asset ([Monitor1],[Monitor2]) values ('" + txtMonitor1.Text + "','" + txtMonitor2.Text + "')", con2)
                    cmd.ExecuteNonQuery()
                    MsgBox("Records Successfully Added!", MsgBoxStyle.Information, "Add New Customer!")
                    txtMonitor1.Text = ""
                    txtMonitor2.Text = ""
                End If
            End Using

            con.Close()
        End If

应该是，当我在列1中搜索1个数据时，它应该检测列1和列2中是否已经存在数据。不只是在column1中。

Answer 1

好吧，如果您想搜索并返回有关字段是否存在的结果，则不应使用 OledbReader ，我也确实注意到reader不是Read（即使在这种情况下使用它也不正确）。您宁愿使用ExecuteScalar来查看字段是否存在（> 0或<0 ）。

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim CMDText As String = ("SELECT COUNT(*) FROM Asset WHERE Monitor1=@Monitor1 AND Monitor2=@Monitor2")
        Dim Found As Integer
        If String.IsNullOrEmpty(txtHostname.Text) Then
            MsgBox("Please fill-up all fields!", MsgBoxStyle.Exclamation, "Inventory!")
        Else
            Using CN As New OleDb.OleDbConnection With {.ConnectionString = "CON_STR"},
                           Cmd1 As New OleDb.OleDbCommand(CMDText, CN)
                CN.Open()
                With Cmd1.Parameters
                    .Add("@Monitor1", OleDb.OleDbType.VarChar).Value = txtMonitor1.Text
                    .Add("@Monitor2", OleDb.OleDbType.VarChar).Value = txtMonitor2.Text
                End With
                Found = Cmd1.ExecuteScalar()
            End Using
            If Found > 0 Then
                ' User already exists
                MsgBox("User Already Exist!", MsgBoxStyle.Exclamation, "Add New User!")
            Else
                Dim CmdText1 As String =
                   ("INSERT INTO Asset (Monitor1,Monitor2) VALUES (@Monitor1 ,@Monitor2)")
                Using Cmd As New OleDb.OleDbCommand(CmdText1, CN)
                    With Cmd.Parameters
                        .Add("@Monitor1", OleDb.OleDbType.VarChar).Value = txtMonitor1.Text
                        .Add("@Monitor2", OleDb.OleDbType.VarChar).Value = txtMonitor2.Text
                    End With
                    Cmd.ExecuteNonQuery()
                    ' User does not exist, add them
                    MsgBox("Records Successfully Added!", MsgBoxStyle.Information, "Add New Customer!")
                    txtMonitor1.Text = String.Empty
                    txtMonitor2.Text = String.Empty
                    Cmd.Parameters.Clear()
                End Using
            End If
        End If
    End Sub

在我的示例代码中：“ CON_STR” =我用来测试代码的ConnectionString，因为您未提供任何代码。

避免跨列重复记录

1 个答案: