get maximum value of a dataset

Hello, I am looking for how to get the maximum value record on my dataset. I found this code

Code:

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(maximumRecord = myDataset.compute("Max(columnName)", ""))

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on google but this is not working with a dataset, it is suppose to work on a table, but I need to get the maximum value of a specific data that I put into a dataset.

DataSets don't have maximum values. In fact, they have no values at all. DataSets contains DataTables. It's the DataTables that contain the columns that describe the data and the rows that contain the data. You can't possibly have put any data directly into a DataSet because it's simply not possible. You have to have put the data into a DataTable, so just call Compute on that DataTable.

well, I can't just call the whole table because I need to calculate the maximum value of a specific data, I'll show you what I got. I am trying to use the maximum value to make a primary key.

Code:

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Dim maximumRecord As String
    Private Sub Load_History()

        Dim fontname As String = "Tahoma"
        Dim fontsize As Integer = "8"
        Dim fnt As New Font(fontname, fontsize, FontStyle.Regular)

        Dim myCnt As Integer

        Dim myStr As String

        Dim myDataset As New DataSet

        myStr = "select * from notes where Orderref='" + txtorderref.Text + "'"

        Dim sqldaHistory As New SqlDataAdapter(myStr, nwindconn)

        sqldaHistory.Fill(myDataset, "notes")

        myCnt = myDataset.Tables(0).Rows.Count
'can't use noteCounter which works but would cause me errors if a row gets deleted, myDataset.Tables(0).Rows.Count method not suitable for PKs
        'noteCounter = myDataset.Tables(0).Rows.Count


        'maximumRecord = myDataset.compute("Max(noteref)", "")
   

        Do While myCnt > 0
            myCnt = myCnt - 1

            Dim lblName As New Label
            'name is not yet on notes table, to be copied from orders owner
            lblName.Text = myDataset.Tables(0).Rows(0).Item("name")
            lblName.Font = fnt

            Dim lblEvent As New Label
            lblEvent.Size = New Size(134, 17)
            'event is on notes but most of the records are empty
            lblEvent.Text = myDataset.Tables(0).Rows(0).Item("Event").ToString
            lblEvent.Font = fnt

            Dim lblNote As New Label
            lblNote.Text = myDataset.Tables(0).Rows(0).Item("note")
            lblNote.Size = New Size(1105, 39)
            lblNote.Font = fnt
            lblNote.AutoSize = True

            pnlNewNote.Controls.Add(lblName)
            pnlNewNote.Controls.Add(lblEvent)
            pnlNewNote.Controls.Add(lblNote)

        Loop

    End Sub

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So I want to get the maximum value from these records:

Code:

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myStr = "select * from notes where Orderref='" + txtorderref.Text + "'"

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I just tried this but I got an error:
An expression of non-boolean type specified in a context where a condition is expected, near 'M0800176 '.

Code:

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Dim db_command As New SqlCommand("select max(NoteRef) as max_NoteRef from notes where '" + txtorderref.Text + "'", nwindconn)
        Label1.Text = db_command.ExecuteScalar()

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That's what I been looking for

Code:

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maximumRecord = myDataset.Tables(0).Compute("Max(noteref)", "")

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