ORA-00904: string: invalid identifier 

Cause: The column name entered is either missing or invalid. 

Action: Enter a valid column name. A valid column name must begin with a letter, 
be less than or equal to 30 characters, and consist of only alphanumeric characters 
and the special characters $, _, and #. If it contains other characters, then it must 
be enclosed in double quotation marks. It may not be a reserved word.  

   set pagesize 25
   set linesize 121

   EXPLAIN PLAN FOR
   < Your Query >;


    SELECT * FROM TABLE(dbms_xplan.display);