[ابو يوسف النواوي 2]

Dim sql4 As String = ""

        sql4 = "SELECT    SUM(اسم_الحقل) AS NetInvoice   FROM dbo.اسم_الجدول"

        Dim adp4 = New SqlClient.SqlDataAdapter(sql4, cn)
        Dim ds4 As New DataSet
        adp4.Fill(ds4)
        Dim dt4 = ds4.Tables(0)

        Dim sum As Integer = 0
        For I As Integer = 0 To dt4.Rows.Count - 1
            sum += Convert.ToInt32(dt4.Rows(I).Item("NetInvoice"))
        Next
        TextBox1.Text = sum.ToString()