Question

我正在使用VB2010 Express，我有一个带有以下字段Ext，CostAssing和CostAct的Mysql平板电脑，我正在尝试从第一个查询中获得的结果更新Mysql表：

首先查询获取Ext和CostAssing
具有CostAssing值的第二个查询更新字段CostAct

**

Imports MySql.Data.MySqlClient
Imports System
Imports System.IO
Public Class Form1
    Public dbconn As New MySqlConnection
    Public sql As String
    Public sqlQuery As String
    Public SQLcmd As MySqlCommand
    Public dbcomm As MySqlCommand
    Public dbread As MySqlDataReader
    Dim Ext As String
    Dim CostAssing As Integer
    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        dbconn = New MySqlConnection("Data Source=localhost ; user id=root ; password=password ; database=calls")
        'First Query Get Extension and CostAssing
          Try
            dbconn.Open()
            sqlQuery = "SELECT Ext,CostAssing FROM estruc "
            SQLcmd = New MySqlCommand(sqlQuery, dbconn)
            dbread = SQLcmd.ExecuteReader
            While dbread.Read()
                Ext = dbread.Item("Ext")
                CostAssing = dbread.Item("CostAssing")
                MsgBox("Ext:" & Ext)
                'Second Query Update Ext from CostAct to CostAssing
                Try
                    sqlQuery = "UPDATE estruc SET CostAct = '" & "1000" & "'  WHERE Ext = '" & Ext & "'"
                    SQLcmd = New MySqlCommand(sqlQuery, dbconn)
                    dbread = SQLcmd.ExecuteReader
                Catch ex As Exception
                    MsgBox("Error 2 is :" & ex.Message)
                End Try
            End While
        Catch ex As Exception
            MsgBox("Error 1 is :" & ex.Message)
        End Try
        dbread.Close()
    End Sub
End Class

**

第一个查询运行正常，我得到字段Ext和CostAssing，但是当第二个Query尝试更新de字段CostAct时，我得到以下错误（由Catch ex As Exception MsgBox报告（“错误2是：”＆amp; ex。消息））：

“错误2是：已经有一个与此Connection关联的打开的Datareader，必须先关闭它。”

PLease，有什么想法吗？

Answer 1

在第一次查询后添加以下行以关闭datareader

dbread.Close();

您希望先存储dbread中的值（数据表或列表等），关闭while循环，然后运行第二个查询：

SQLcmd.ExecuteNonQuery();

请参阅this similar question

Visual Basic 2010和Mysql嵌套查询

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