How to Fix the ORA-00904 'Invalid Identifier' Error in Oracle SQL?

Troubleshooting the Oracle "ORA-00904: Invalid Identifier" Error

The frustrating "ORA-00904: Invalid Identifier" error in Oracle databases typically stems from incorrect referencing of database objects (tables or columns). This often involves case sensitivity and the use of double quotes.

Let's examine a sample inner join query:

<code class="language-sql">SELECT Employee.EMPLID as EmpID,
Employee.FIRST_NAME AS Name,
Team.DEPARTMENT_CODE AS TeamID,
Team.Department_Name AS teamname
FROM PS_TBL_EMPLOYEE_DETAILS Employee
INNER JOIN PS_TBL_DEPARTMENT_DETAILS Team
ON Team.DEPARTMENT_CODE = Employee.DEPTID</code>

The error arises because the table "Team" and its columns ("DEPARTMENT_CODE" and "Department_Name") might be inconsistently cased. Oracle's case-sensitive nature demands exact matching when double quotes are used during object creation. Using "Department_Code" instead of "DEPARTMENT_CODE" will trigger the ORA-00904 error:

<code class="language-sql">SQL> select count(*) from PS_TBL_DEPARTMENT_DETAILS
where Department_Code = 'BAH'
/
ERROR at line 2:
ORA-00904: "DEPARTMENT_CODE": invalid identifier

SQL> select count(*) from PS_TBL_DEPARTMENT_DETAILS
where "Department_Code" = 'BAH'
/

COUNT(*)
----------
0

SQL></code>

Avoiding double quotes during table creation simplifies object referencing, allowing for case-insensitive access:

<code class="language-sql">create table PS_TBL_DEPARTMENT_DETAILS
( company_code VARCHAR2(255),
company_name VARCHAR2(255),
Cost_Center_Number VARCHAR2(255))
;

select * from ps_tbl_department_details</code>

Best practice: Minimize double quote usage in DDL scripts to prevent case-sensitive referencing issues and simplify database object access.

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