Question

Dim sql As String = "Select ProductID From OrderDetail Order By ProductID Desc"
    Dim command As New SqlCommand(sql, connection)
    Dim reader1 As SqlDataReader = command.ExecuteReader()

How do i store all the productid that i have retrieve into an array?

Answer 1

Dim list As New List(Of Integer)

Using reader As SqlDataReader = command .ExecuteReader()
    While reader.Read()
        list.Add(reader.GetInt32(reader.GetOrdinal("ProductID")))
    End While
End Using
'check  list.ToArray() now

EDIT : But, Instead of return an Array, i Would return a Generic List of Integers (if you only want to return the ProductId) or A List of ProductClass objects

Private Function GetProductIDs() As IList(Of Integer)

    Dim list As New List(Of Integer)
    Dim conStr = "write your connection string here"

    Using connection As New SqlConnection(conStr )
        Dim sql As String = "Select ProductID From OrderDetail Order By ProductID Desc"
        Dim command As New SqlCommand(sql, connection)
        Using reader As SqlDataReader = command.ExecuteReader()
            While reader.Read()
                list.Add(reader.GetInt32(reader.GetOrdinal("ProductID")))
            End While
        End Using
    End Using

    Return list

End Function

EDIT 2 : As per the comment,
To retrieve an put in the Text of a label, you can do this

Dim str As String
str = String.Join(",", GetProductIDs())
Label1.Text=str;

Assuming Label1 is theI D of your label control.The String.Join method will return a string of ProductId’s seperated by comma like "1,2,6,7"