Organizar duplicados y numerar los registros en una secuencia - MySQL

Prueba:

SELECT t1.id, t1.name, t1.account
       , (SELECT COUNT(*)
            FROM tableName t2
           WHERE t2.name = t1.name
             AND t2.account = t1.account
             AND t2.id <= t1.id) AS dupno
  FROM tableName t1;

Salida:

ID NAME ACCOUNT DUPNO
-- ---- ------- -----
 1 ABC  PQR         1 
 2 DEF  PQR         1 
 3 ABC  PQR         2 
 4 XYZ  ABC         1 
 5 DEF  PQR         2 
 6 DEF  ABC         1