SELECT ACCT_ID, SUM( INV_31_60 ) AS INV_31_60
FROM INVOICES
WHERE COLLECTOR_ID = 1
HAVING SUM( INV_31_60 ) < (
     SELECT SUM( INV_31_60 )
     FROM `INVOICES`
     WHERE COLLECTOR_ID =1
     AND ACCT_ID = 'AT100378'
     )
GROUP BY ACCT_ID
ORDER BY INV_31_60  DESC