How to find rows that do not match between two tables P and N
SELECT N.* 
FROM new_table N 
LEFT JOIN previous_table P 
     ON P.item_id = N.item_id 
    AND P.column_1 = N.column_1
    AND P.column_2 = N.column_2
    AND /* ... */ P.column_n = N.column_N
WHERE P.item_id IS NULL;


or

SELECT N.* 
FROM new_table N 
LEFT JOIN previous_table P 
     ON (P.item_id, P.column_1, P.column_2, /* ... , */ P.column_N) 
       =
        (N.item_id, N.column_1, N.column_2, /* ... , */ N.column_N) 
WHERE P.item_id IS NULL;