def lower_column(col):
    """ Return column from lower level tables if possible

    >>> metadata = sa.MetaData()

    >>> s = sa.Table('accounts', metadata,
    ...              sa.Column('name', sa.String),
    ...              sa.Column('amount', sa.Integer),
    ...              sa.Column('id', sa.Integer, primary_key=True),
    ...              )

    >>> s2 = select([s])
    >>> s2.c.amount is s.c.amount
    False

    >>> lower_column(s2.c.amount) is s.c.amount
    True

    >>> lower_column(s2.c.amount)
    Column('amount', Integer(), table=<accounts>)
    """
    old = None
    while col is not None and col is not old:
        old = col
        if not hasattr(col, 'table') or not hasattr(col.table, 'froms'):
            return col
        for f in col.table.froms:
            if f.corresponding_column(col) is not None:
                col = f.corresponding_column(col)
    return old
