Most people get ORA-00904 because they forgot to put quotes around a literal string in their SQL.

Example:

[code language=”sql”]SQL> select foo from dual;
select foo from dual
*
ERROR at line 1:
ORA-00904: "FOO": invalid identifier

SQL> select ‘foo’ from dual;
‘FOO’
——————————–
foo
[/code]

Other causes of this error may include:

• No privileges on the object in question
• the object or column is misspelled
• There is no private or public synonym, so the object must be called using a fully-qualified name (SCOTT.EMP vs. EMP)