SELECT A.order_number, A.header_id, B.line_id, B.quantity, C.hold_price_id, C.released_flag
FROM Table_A a,
Table_B b,
Table_C c
WHERE a.header_id = b.header_id
AND c.line_id = b.line_id
AND a.header_id = c.header_id
AND a.order_number = '123';