存储为 vb.net 变量的多个 SQL 查询

Question

我知道还有其他一些关于将 sql 结果放入 vb.net 变量的帖子，但我无法理解他们是如何做到的，以及我如何在我的项目中做到这一点。

所以我要做的是在我的数据库中查询 4 ​​个不同的值，然后在表单的某个部分显示每个值。我打算将每个值存储到一个变量中，然后执行 textbox1.text = i

2014 年 10 月 5 日更新代码

 Private Sub LBmembers_SelectedIndexChanged(sender As Object, e As EventArgs) Handles LBmembers.SelectedIndexChanged

    Dim i As String = LBmembers.SelectedItem
    Dim dbProvider = "PROVIDER=Microsoft.Jet.OLEDB.4.0;"
    Dim dbSource = "Data Source= C:\members.mdb "
    Dim SqlQuery As String = "SELECT StartTime, EndTime, ShipCode, CycleTime, WorkPercent, Share FROM tblMembers WHERE Member = @ID;"
    Using con = New OleDb.OleDbConnection(dbProvider & dbSource)
        Using cmd = New OleDb.OleDbCommand(SqlQuery, con)
            con.Open()
            cmd.Parameters.AddWithValue("@ID", OleDb.OleDbType.VarWChar).Value = i
            Using reader = cmd.ExecuteReader()
                If reader.Read() Then
                    TBtimestart.Text = reader.ToString(0)
                    TBtimeend.Text = reader.ToString(1)
                    Dim j = Convert.ToInt32(reader.ToString(2))
                    TBtimecycle.Text = reader.GetInt32(3).ToString
                    TBmemberpercent.Text = reader.GetInt32(4)
                    TBmembershare.Text = reader.GetInt32(5)
                    If j = 1 Then
                        RBpro.Checked = True
                    ElseIf j = 2 Then
                        RBret.Checked = True
                    ElseIf j = 3 Then
                        RBcov.Checked = True
                    ElseIf j = 4 Then
                        RBskiff.Checked = True
                    ElseIf j = 5 Then
                        RBmack.Checked = True
                    ElseIf j = 6 Then
                        RBhulk.Checked = True
                    Else
                        RBpro.Checked = False
                        RBret.Checked = False
                        RBcov.Checked = False
                        RBskiff.Checked = False
                        RBmack.Checked = False
                        RBhulk.Checked = False
                        Exit Sub
                    End If
                End If
            End Using
            con.Close()
        End Using
    End Using
End Sub

例外

InvalidCastException 未处理 指定的强制转换无效。

弹出就行 T​​Btimecycle.text = reader.GetInt32(3).ToString

当我在 using 语句中插入测试代码“TBgrossisk.Text = reader.ToString()”时，阅读器也在读取“System.Data.OleDb.OleDbDataReader”

Answer 1

如果您仔细查看SELECT 语句的语法，您会发现只需一个查询即可请求表的任何列。

Private Sub ListBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles LBmembers.SelectedIndexChanged
    if string.IsNullOrWitheSpace(ListBox1.SelectedItem.ToString()) Then
        MessageBox.Show("Select an item from the Listbox")
    End If

    Dim member As String = ListBox1.SelectedItem
    Dim dbProvider = "PROVIDER=Microsoft.Jet.OLEDB.4.0;"
    Dim dbSource = "Data Source= C:\members.mdb "
    Dim SqlQuery As String = "SELECT StartTime, EndTime, ShipCode, CycleTime " & _ 
                             "FROM tblMembers WHERE Member = @ID;"
    Using con = New OleDb.OleDbConnection(dbProvider & dbSource)
        Using cmd = New OleDb.OleDbCommand(SqlQuery, con)
            con.Open()
            cmd.Parameters.AddWithValue("@ID", OleDb.OleDbType.VarWChar).Value = member
            Using reader = cmd.ExecuteReader
               if reader.Read() Then
                  TextBox1.Text = reader.GetString(0)
                  TextBox2.Text = reader.GetString(1)
                  Dim j = reader.GetInt32(2)
                  If j = 1 Then
                      Radio1.Checked = True
                  ElseIf j = 2 Then
                      Radio2.Checked = True
                  ElseIf j = 3 Then
                      Radio3.Checked = True
                  ElseIf j = 4 Then
                      Radio4.Checked = True
                  ElseIf j = 5 Then
                      Radio5.Checked = True
                  ElseIf j = 6 Then
                      Radio6.Checked = True
                  Else
                      Exit Sub
                  End If
                  TextBox4.Text = reader.GetInt32(3).ToString()
               Else
                  MessageBox.Show("The search for '" & member & "' doesn't find any data")
               End If
           End Using
        End Using
    End Using
End Sub

您可以使用ExecuteReader 方法返回的OleDbDataReader，而不是使用仅返回检索到的第一行的第一列的 ExecuteScalar。该对象允许使用索引（或列名）访问当前记录中的各个列。在 MSDN 中阅读有关 OleDbDataReader 的更多信息