WITH guess_string 
/* 
   Automatic Solution Generator for 
   PL/SQL Challenge's version of Mastermind (plsqlchallenge.oracle.com) 
        
   Author: James Su 
 
   Requires Oracle Database 11g Release 2 or higher. (10g-compatible version follows) 
        
   Permission granted by author to publish this code make it available to others to 
   use and modify to their own purposes. 
*/ 
     AS (SELECT '7654PN,7126PN,4152NN' g_str FROM DUAL), 
     g 
     AS (    SELECT LEVEL lvl, 
                    UPPER (REPLACE (REGEXP_SUBSTR (g_str, 
                                                   '[^,]+', 
                                                   1, 
                                                   LEVEL), 
                                    ' ')) 
                       g_str 
               FROM guess_string 
         CONNECT BY LEVEL <= REGEXP_COUNT (g_str, ',') + 1), 
     t (s, lvl) 
     AS (    SELECT REPLACE (SYS_CONNECT_BY_PATH (n, '/'), '/'), 1 
               FROM (    SELECT LEVEL n 
                           FROM DUAL 
                     CONNECT BY LEVEL <= 7) 
              WHERE LEVEL = 4 
         CONNECT BY NOCYCLE n <> PRIOR n 
         UNION ALL 
         SELECT t.s, t.lvl + 1 
           FROM t, g 
          WHERE     t.lvl = g.lvl 
                AND   4 
                    - NVL ( 
                         LENGTH ( 
                            TRANSLATE (t.s, '@' || g.g_str, '@')), 
                         0) = LENGTH (SUBSTR (g.g_str, 5)) 
                AND   DECODE (SUBSTR (t.s, 1, 1), 
                              SUBSTR (g.g_str, 1, 1), 1, 
                              0) 
                    + DECODE (SUBSTR (t.s, 2, 1), 
                              SUBSTR (g.g_str, 2, 1), 1, 
                              0) 
                    + DECODE (SUBSTR (t.s, 3, 1), 
                              SUBSTR (g.g_str, 3, 1), 1, 
                              0) 
                    + DECODE (SUBSTR (t.s, 4, 1), 
                              SUBSTR (g.g_str, 4, 1), 1, 
                              0) = REGEXP_COUNT (g.g_str, 'P')) 
SELECT t.s 
  FROM t 
 WHERE lvl = 
          (SELECT REGEXP_COUNT (g_str, ',') + 2 
             FROM guess_string)