关于数据库查询的问题

[angelo_2574]

总是出错，“未处理的OleDbException ,至少一个参数没有被指定值。”怎么也找不出来，麻烦高手！
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
If Trim(txtID.Text) = "" Then
MsgBox("输入要查询的学生学号！", MsgBoxStyle.Critical, "提示")
Else
myconnection.Open() '打开数据库
Dim mycommandtext As String
mycommandtext = "select * from student where 学号＝" & Trim(txtID.Text) 'SQL查询命令
mycommand.CommandText = mycommandtext
mycommand.Connection = myconnection '命令对应的连接对象


Dim myadapter As New OleDbDataAdapter(mycommand)
Dim mydataset As New DataSet
myadapter.Fill(mydataset, "result")
DataGridView1.DataSource = mydataset.Tables("result")
End If
End Sub

[angelo_2574]

myconnection和mycommand是全局对象，数据库的连接对象myconnection已经设置好了，

Public Class Form1

Dim myconnection As New OleDbConnection 'DB连接对象
Dim mycommand As New OleDbCommand '数据库命令


Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim connectionstring As String
connectionstring = "provider=microsoft.jet.oledb.4.0; data source=F:\Visual Studio 2008" + _
"\Projects\ziji_通过编程的方式访问ACCESS数据库，并实现查询、插入、删除等操作\" + _
"ziji_通过编程的方式访问ACCESS数据库，并实现查询、插入、删除等操作\bin\student.mdb"
myconnection.ConnectionString = connectionstring


End Sub

[changjiangzhibin]

'没看到什么错误，提几点建议吧
Public Class Form1 

    Dim myconnection As New OleDbConnection  'DB连接对象 
    Dim mycommand As New OleDbCommand            '数据库命令 
    

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load 
        Dim connectionstring As String 
        connectionstring = "provider=microsoft.jet.oledb.4.0; data source=F:\Visual Studio 2008" + _ 
        "\Projects\ziji_通过编程的方式访问ACCESS数据库，并实现查询、插入、删除等操作\" + _ 
        "ziji_通过编程的方式访问ACCESS数据库，并实现查询、插入、删除等操作\bin\student.mdb" 
        myconnection.ConnectionString = connectionstring 
'这种数据库路径是第一次见到，建议改简单些

    End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click 
        If Trim(txtID.Text) = "" Then          
            MsgBox("输入要查询的学生学号！", MsgBoxStyle.Critical, "提示") 
        Else 
            myconnection.Open()      '打开数据库 
            Dim mycommandtext As String 
            mycommandtext = "select * from student where 学号＝" & Trim(txtID.Text) 'SQL查询命令 
            mycommand.CommandText = mycommandtext 
            mycommand.Connection = myconnection      '命令对应的连接对象 


            Dim myadapter As New OleDbDataAdapter(mycommand) 
            Dim mydataset As New DataSet 
            myadapter.Fill(mydataset, "result") 
            DataGridView1.DataSource = mydataset.Tables("result") 
　　　　　'上面这一句，一般这样写，如下
　　　　　　　DataGridView1.DataSource = mydataset.Tables[0].DefaultView
            DataGridView1.DataBind();
        End If 
    End Sub

[pinyu]

莫非你输入的学号里有@这个符号？用户输入的学号是什么？

[pinyu]

对了，建议你注释掉myconnection.open。问题多半就得以解决。你解决了问题我告诉你原因，因为我还不太确定

[amandag]

mycommandtext = "select * from student where 学号＝" & Trim(txtID.Text) 'SQL查询命令
==
mycommandtext = "select * from student where 学号＝'" & Trim(txtID.Text) & "'" 'SQL查询命令

[angelo_2574]

没有用啊，还是同样的错误，郁闷！

[angelo_2574]

高手啊！帮忙解决下咯！