How would you resolve ORA-00904: “invalid identifier” error in Oracle database?

How to Resolve ORA-00904: "Invalid Identifier" Error in Oracle Database

When encountering the ORA-00904 error in an Oracle database, it means that the column name entered is either missing or invalid. Here are some steps to resolve this issue:

1. Check the SQL query: Review the SQL query being executed and ensure that all column names referenced in the query are spelled correctly and exist in the database schema.
2. Use double quotes: If the column name contains special characters or is case-sensitive, enclose the column name in double quotes in the SQL query.
3. Check table alias: If the column is referenced using a table alias, make sure that the alias is correctly defined and used in the query.
4. Verify table and column names: Verify that the table and column names are correct and properly qualified with the schema name, if necessary.
5. Check for synonym usage: If synonyms are being used, ensure that the synonym is pointing to the correct table or column.

By following these steps and identifying the root cause of the ORA-00904 error, you can effectively resolve the issue and ensure the smooth operation of your Oracle database.