SQL> create or replace directory BDUMP as 'C:\oracle\product\10.2.0\dbtest\admin\dbtest\bdump';

SQL> CREATE TABLE ALERT_LOG ( MSG VARCHAR2(255) )
         ORGANIZATION EXTERNAL (
                 TYPE ORACLE_LOADER
                 DEFAULT DIRECTORY BDUMP
                 ACCESS PARAMETERS ( records delimited by newline
                 )
                 LOCATION (BDUMP:'alert_dbtest.log')
        )
        REJECT LIMIT UNLIMITED NOPARALLEL NOMONITORING; 

SQL> SELECT msg FROM alert_log WHERE msg LIKE '%ORA-%';

SQL> SELECT msg FROM alert_log WHERE msg LIKE '%WARNING:%' OR msg like '%WARNING -%';