Question

我有一个女士访问数据库，其中包含40名学生，我想找到至少18岁的学生。

我尝试使用此代码，但是它不起作用！

Try
    DataGridView1.Rows.Clear()
    Dim dt As DataTable = New DBConnect().selectdata(String.Format("SELECT ID, Name FROM Students where Age > %{0}%", FlatTextBox8.Text))
    For i As Integer = 0 To dt.Rows.Count - 1
        DataGridView1.Rows.Add(i + 1, dt.Rows(i)(0), dt.Rows(i)(1))
    Next
    dt.Dispose()
    dt = Nothing
Catch ex As Exception

End Try

我该怎么做？

Answer 1

名称是保留字，请尝试：

String.Format("SELECT ID, [Name] FROM Students where Age > {0}", FlatTextBox8.Text))

也就是说，使用参数。

Answer 2

最好使用参数化查询以避免sql注入。

此小功能将填充并返回一个DataTable，其中包含您正在查看的值！

Private Function GetData() As System.Data.DataTable
    Dim dt As New DataTable
    Dim sqlCmd As String = "SELECT ID, Name FROM Students where Age > @Age"
    Using myConnection As New SqlConnection(your_connection_string)
        myConnection.Open()
        Using myDataAdapter As New SqlDataAdapter(sqlCmd, myConnection)
            myDataAdapter.SelectCommand.Parameters.Add("@Age", SqlDbType.Int) 'Change the type if your DB Table has another type
            myDataAdapter.SelectCommand.Parameters("@Age").Value = Convert.ToInt16(FlatTextBox8.Text) 'Change the type if your DB Table has another type
            myDataAdapter.Fill(dt)
        End Using
        myConnection.Close()
    End Using
    Return dt
End Function

现在是时候在代码中调用它了：

Try
    DataGridView1.Rows.Clear()
    Dim dt As DataTable = GetData()
    For i As Integer = 0 To dt.Rows.Count - 1
        DataGridView1.Rows.Add(i + 1, dt.Rows(i)(0), dt.Rows(i)(1))
    Next
    dt.Dispose()
    dt = Nothing
Catch ex As Exception
    MsgBox(ex.Message)
    Err.Clear
End Try

您会注意到，我还添加了一个MsgBox()，如果引发异常，它将向您显示错误消息。我发现这在调试时非常有用。

女士访问“大于”或相等查询

2 个答案: