ORA-00904

Title :

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.