ORA-00904: Invalid Identifier
1. Typographical Errors: Incorrect spelling or case sensitivity of table names, column names, or aliases.
2. Missing or Renamed Objects: Referencing objects (tables, views, columns) that do not exist in the database.
3. Ambiguous Column Names: Using column names that exist in multiple tables without proper qualification.
4. Reserved Keywords: Using Oracle reserved keywords as identifiers without proper escaping.
5. Incorrect Schema or Owner: Referencing objects in a different schema without qualifying the object name correctly.
SELECT employee_name, empolyee_id FROM employees; -- ORA-00904: "EMPOLYEE_ID": invalid identifier
Here, "empolyee_id " is misspelled as "empolyee_id," causing an ORA-00904 error.
empolyee_id
ORA-00904
SELECT id FROM employees JOIN departments USING (id); -- ORA-00904: "ID": invalid identifier
Here, "id" is ambiguous because it exists in both the "employees" and "departments" tables.
id
employees
departments
To resolve the ORA-00904 error:
1. Check and correct any spelling errors in your SQL statements.
2. Ensure that all referenced objects (tables, columns) exist in the database.
3. Use table aliases or fully qualify column names to avoid ambiguity.
4. Enclose reserved keywords in double quotes if they are used as identifiers.
5. Verify the correct schema or owner of the objects being referenced.