Why Am I Getting the ORA-00904 Error in My Oracle Inner Join Queries?

Oracle's ORA-00904 Error: Invalid Identifier in Inner Joins

Oracle users frequently encounter the "ORA-00904: invalid identifier" error when executing inner join queries. This error commonly stems from inconsistent use of double quotes when referencing database objects (tables and columns).

For example, if a table, such as "PS_TBL_DEPARTMENT_DETAILS," is created using double quotes around its name, all subsequent references to that table and its columns must also include double quotes. Omitting these quotes will trigger the "invalid identifier" error. Oracle strictly enforces case sensitivity when double quotes are used; the case and quoting must precisely match the original definition.

Solutions and Best Practices

The solution involves either removing double quotes from the table creation statement or ensuring consistent use of double quotes in all references.

To avoid case-sensitivity problems altogether, it's recommended to create database objects using uppercase names without double quotes. This allows for case-insensitive referencing.

Illustrative Example:

Let's create the table without double quotes:

<code class="language-sql">CREATE TABLE PS_TBL_DEPARTMENT_DETAILS (
  DEPTID VARCHAR2(255) PRIMARY KEY,
  DEPT_NAME VARCHAR2(255)
);</code>

Now, queries can be written in any case without double quotes:

<code class="language-sql">SELECT * FROM PS_TBL_DEPARTMENT_DETAILS;
SELECT dept_name FROM PS_TBL_DEPARTMENT_DETAILS WHERE deptid = 'BAH';</code>

Key Takeaway: To prevent ORA-00904 errors and maintain code clarity, avoid using double quotes in your Data Definition Language (DDL) scripts whenever possible. Using uppercase names without quotes is the best practice for avoiding case-sensitivity issues.

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