mysql - 错误: Unable to cast object of type 'System.Int64' to type 'System.Data.Odbc.OdbcDataReader'

Question

我正在尝试计算已保存数据的记录数。
这是我的代码:

    Dim pl_qry As String
    Dim pl_cmd As New Odbc.OdbcCommand
    Dim pl_dr As Odbc.OdbcDataReader

    If txtPurpose.Text = "PERSONAL LOAN" Then
        pl_qry = "select count(purpose) from details where borrower_id = '" & bor_id & "' and purpose = '" & "PERSONAL LOAN" & "'"
        pl_cmd.CommandText = pl_qry
        pl_cmd.Connection = con
        pl_dr = pl_cmd.ExecuteScalar

        pl_dr.Read()
        If Not pl_dr.IsDBNull(0) Then
            MsgBox(pl_dr.GetString(0))
        End If
    End If

我在这一行遇到了错误

    pl_dr = pl_cmd.ExecuteScalar 

Answer 1

如果您已检查 ExecuteScalar方法，您会注意到它将返回 SQL 第一行的第一列。

问题是您已将结果分配给“OdbcDataReader”

Dim pl_dr As Odbc.OdbcDataReader

但也许你可以直接得到结果:

Int64 result = Convert.ToInt64(cmd.ExecuteScalar())