Question

嘿朋友我正在使用带有* 组合框 *的表单，其中我从中获取的项目 sqldatabase命名为balance，sqldatabase有两列，一列是customername和另一个是现在的不平衡。

在表格中，我已经从表格中绑定了所有客户名称，现在我有一个我想要做的文本框当用户选择combobox.selected项时，任何一个客户名称我需要在tat文本框中显示所选客户的不平衡

Ihad使用了datareader，但它显示错误，你可以帮助我........

    Dim ST As String = ComboBox1.SelectedItem

    Dim sqlcon As New SqlConnection(conectionstring)

    Dim sqlcmd As New SqlCommand("SELECT OBBALANCE FROM BALANCE WHERE CUSTOMERNAME =  " & " '" & ST & "'" & "", sqlcon)
    Dim sdr As New SqlDataReader


    Try
        con.Open()
        sdr = sqlcmd.ExecuteReader
        While (sdr.Read())
            Textbox7.Text = sdr[1]

        End While
    Catch ex As SqlException
        MessageBox.Show(ex.Message)

    End Try

Icant了解如何阅读plz帮我读取数据，表中首先是列名，接下来是obbalance字段

Answer 1

由于您要从数据库中读取单个值，因此请使用 ExecuteScalar 方法而不是使用datareader。

Dim ST As String = ComboBox1.SelectedText 

Dim sqlcon As New SqlConnection(conectionstring)

Dim sqlcmd As New SqlCommand("SELECT OBBALANCE FROM BALANCE WHERE CUSTOMERNAME = '" & ST & "'" , sqlcon)
Dim result as Object

Try
    con.Open()

    result = sqlcmd.ExecuteScalar()

    If result IsNot Nothing Then
         Textbox7.Text = result.ToString() 
    End If

Catch ex As SqlException
    MessageBox.Show(ex.Message)     

End Try

<强>更新
修改代码以检查null 删除了不再需要的datareader对象从查询中删除了不必要的字符。

Answer 2

Dim ST As String = ComboBox1.SelectedText 

    Dim sqlcon As New SqlConnection(conectionstring)

    Dim sqlcmd As New SqlCommand("SELECT OBBALANCE FROM BALANCE WHERE CUSTOMERNAME =  " & " '" & ST & "'" & "", sqlcon)
  Dim sdr As SqlDataReader


    Try
        sqlcon.Open() 'edited
        sdr = sqlcmd.ExecuteReader()
        While (sdr.Read())
            TextBox1.Text = sdr("OBBALANCE").ToString() 'sdr(1) is wrong since there is only one item
        End While
    Catch ex As SqlException
        MessageBox.Show(ex.Message)


    End Try

如何在获取文本框的值时使用datareader

2 个答案: