VB.NET：使用变量生成MySQL查询

Question

I have written the code below to update my table, but it doesn't work.

sqlstr = "UPDATE Student SET " & S & " = @field1, " & L & " = @field2, " & R & " =@field3, " & W & "=@field4 WHERE Code='" & StdID & "'"
DBCmd = New MySql.Data.MySqlClient.MySqlCommand(sqlstr, DBConn)
With DBCmd
        .Parameters.AddWithValue("@field1", CB_S.SelectedItem)
        .Parameters.AddWithValue("@field2", CB_L.SelectedItem)
        .Parameters.AddWithValue("@field3", CB_R.SelectedItem)
        .Parameters.AddWithValue("@field4", CB_W.SelectedItem)
    End With
    DBCmd.Dispose()

Where S, L, R and W are strings: S1, L1, R1, W1. And StdID is an integer. CB_S, CB_L, CB_R and CB_W are comboboxes.

Could anyone tell me what is wrong?

Answer 1

you did not open the connection and call ExecuteNonQUery() . Also parameterized the value for Code

sqlstr = "UPDATE Student SET " & S & " = @field1, " & L & " = @field2, " & R & " =@field3, " & W & "=@field4 WHERE Code=@code"
DBCmd = New MySql.Data.MySqlClient.MySqlCommand(sqlstr, DBConn)
With DBCmd
        .Parameters.AddWithValue("@field1", CB_S.SelectedItem)
        .Parameters.AddWithValue("@field2", CB_L.SelectedItem)
        .Parameters.AddWithValue("@field3", CB_R.SelectedItem)
        .Parameters.AddWithValue("@field4", CB_W.SelectedItem)
        .Parameters.AddWithValue("@code", StdID)
End With
DBConn.Open()
DBCmd.ExecuteNonQuery()