小弟这几天在写一个图书管理软件，下面代码是借书按键的功能实现。
不过出现了一个问题：下面的代码中"update tblbook set amount=amount-1 where bookID='" & Trim(Txtbookid2.Text) & "'"这一句执行了两次。
比如：原来数据是10，我按了按钮后想让它等于9，可是当我按钮后却等于8.
sql语句我验证过没错，不知道是哪里发生的错误。
大侠们请帮帮我啊~~~~~~555......
Private Sub Btbrw_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Btbrw.Click
'如果是借书时确认，即“借书”按钮已经变成了“确认”按钮
If Btbrw.Text = "确认" Then
'保存借书时当前显示的记录号
Dim currentPos As Integer = Me.BindingContext(Ds2, "tblborrow").Position
'弹出警告框，如果用户单击“确定”，那么
If MessageBox.Show("确定借书吗？", "借书－确认", MessageBoxButtons.OKCancel) = DialogResult.OK Then
If Trim(Txtbookid2.Text) = "" Then
MessageBox.Show("书的编号不能为空！")
Return
End If
Dim selshlid As String = "select * from tblbook where amount='0' and bookID='" & Trim(Txtbookid2.Text) & "'"
'打开连接，并执行查询
OleDbConnection2.Open()
ODAcmd2.SelectCommand.CommandText = selshlid
ODAcmd2.SelectCommand.ExecuteNonQuery()
'重新填充数据集，并关闭连接
Ds.Clear()
ODAcmd2.Fill(Ds, "tblbook")
OleDbConnection2.Close()
Dim iCnt As Integer
Dim iPos As Integer
'总共有多少条记录
iCnt = Me.BindingContext(Ds, "tblbook").Count
If iCnt = 0 Then
Dim scertificateid As String = "'" & TxtshlID.Text & "'"
Dim slibid As String = "'" & TxtlibID.Text & "'"
Dim sname As String = "'" & Txtname.Text & "'"
Dim sbookid As String = "'" & Txtbookid2.Text & "'"
Dim sbookname As String = "'" & Txtbookname2.Text & "'"
Dim sborrowdate As String = "'" & Txtbrwdate.Text & "'"
Dim sreturn As String = "'" & Txtrtdate.Text & "'"
'定义插入记录的SQL语句
Dim addstr As String = "insert into tblborrow (certificateID,libID,name,bookID,bookname,borrowDate,return) values ("
addstr = addstr & scertificateid & "," & slibid & ","
addstr = addstr & sname & "," & sbookid & ","
addstr = addstr & sbookname & "," & sborrowdate & ","
addstr = addstr & sreturn & ")"
'' MessageBox.Show(addstr)
'打开连接
OleDbConnection2.Open()
'设置InsertCommand需要执行的SQL语句
ODAcmd3.InsertCommand.CommandText = addstr
'执行插入
ODAcmd3.InsertCommand.ExecuteNonQuery()
'清空数据集
Ds2.Clear()
'重新从数据库获取最新记录来填充数据集
ODAcmd3.Fill(Ds2)
'显示最后一个记录，也就是刚刚添加的记录
Me.BindingContext(Ds2, "tblborrow").Position = Me.BindingContext(Ds2, "tblborrow").Count
'关闭连接
OleDbConnection2.Close()
Dim upamount As String = "update tblbook set amount=amount-1 where bookID='" & Trim(Txtbookid2.Text) & "'"
'打开连接，并执行查询
OleDbConnection2.Open()
ODAcmd2.SelectCommand.CommandText = upamount
ODAcmd2.SelectCommand.ExecuteNonQuery()
'重新填充数据集，并关闭连接
Ds.Clear()
ODAcmd2.Fill(Ds, "tblbook")
OleDbConnection2.Close()
Else
'如果多于0条
MessageBox.Show("对不起，你所要借的书已经全部借出，请过几天再来看看.", "无法借阅－确认", MessageBoxButtons.OK)
Txtbrwdate.Text = ""
'清空还书日期
Txtrtdate.Text = ""
TxtshlID.Text = ""
TxtlibID.Text = ""
Txtname.Text = ""
Txtbookid2.Text = ""
Txtbookname2.Text = "
'显示单击“添加”按钮前显示的记录
Me.BindingContext(Ds2, "tblborrow").Position = currentPos
End If
Else '如果用户在弹出警告框时单击“取消”按钮
'重新填充数据集
'Ds2.Clear()
'ODAcmd3.Fill(Ds2)
'清空借阅日期
Txtbrwdate.Text = ""
'清空还书日期
Txtrtdate.Text = ""
'显示单击“添加”按钮前显示的记录
Me.BindingContext(Ds2, "tblborrow").Position = currentPos
End If
'确认后，不管是取消还是确定，都恢复到单击“添加”按钮前的状态
ShowPosition() '显示记录的位置信息
Btbrw.Text = "借书" '按钮又恢复成“添加”
Btreturn.Enabled = True '“还书”按钮可用
setall(True) '文本框只读，不相关按钮可用
Return
End If
'如果是“借书”按钮，即第一次单击该按钮
If Btbrw.Text = "借书" Then
'文本框置空
TxtshlID.Text = ""
TxtlibID.Text = ""
Txtname.Text = ""
Txtbookid2.Text = ""
Txtbookname2.Text = ""
Txtrtdate.Text = "未还"
'申请号获取当前日期
Dim t As Date = Date.Now
Dim s As String = t.Date
Txtbrwdate.Text = s
'改变为确认按钮
Btbrw.Text = "确认"
Btreturn.Enabled = False
'文本框可写，并且不相关的按钮不可用
setall(False)
'结束该过程
Return
End If
End Sub
