Oracle/PLSQL: ORA-00904 Error

Error:

ORA-00904: invalid column name

Cause:

You tried to execute an SQL statement that included an invalid column name or the column name is missing.

Action:

The options to resolve this Oracle error are:

Rewrite your SQL to include a valid column name. To be a valid column name the following criteria must be met:
- The column name must begin with a letter.
- The column name can not be longer than 30 characters.
- The column name must be made up of alphanumeric characters or the following special characters: $, _, and #. If the column name uses any other characters, it must be enclosed in double quotation marks.
- The column name can not be a reserved word.