Question i am trying to find diff between two line of purchase order in oracle procurment bussiness help me to write a sql query to find

SELECT
    pl.po_header_id,
    pl.po_line_id,
    pl.item_id,
    pl.unit_price AS current_unit_price,
    pl_prev.unit_price AS previous_unit_price,
    (pl.unit_price - pl_prev.unit_price) AS price_difference
FROM
    po_lines_archive_all pl
    LEFT JOIN (
        SELECT
            po_header_id,
            po_line_id,
            item_id,
            unit_price,
            MAX(to_co_seq) AS previous_to_co_seq
        FROM
            po_lines_archive_all
        WHERE
            to_co_seq < (
                SELECT
                    MAX(to_co_seq)
                FROM
                    po_lines_archive_all
                WHERE
                    po_header_id = pl.po_header_id
                    AND po_line_id = pl.po_line_id
            )
        GROUP BY
            po_header_id,
            po_line_id,
            item_id,
            unit_price
    ) pl_prev ON pl.po_header_id = pl_prev.po_header_id
        AND pl.po_line_id = pl_prev.po_line_id
        AND pl.item_id = pl_prev.item_id
WHERE
    pl.po_header_id = :po_header_id

here is the code this is i am try can you help me to find diff