title: ORA-00904: invalid identifier
body: <p>I tried to write the following inner join query using an Oracle database:</p>
  
  <pre><code> 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></pre>
  
  <p>That gives the below error:</p>
  
  <pre><code> INNER JOIN PS_TBL_DEPARTMENT_DETAILS Team ON Team.DEPARTMENT_CODE = Employee.DEPTID
                                                *
  ERROR at line 4:
  ORA-00904: "TEAM"."DEPARTMENT_CODE": invalid identifier
  </code></pre>
  
  <p>The DDL of one table is:</p>
  
  <pre><code>CREATE TABLE "HRMS"."PS_TBL_DEPARTMENT_DETAILS"
  (
    "Company Code" VARCHAR2(255),
    "Company Name" VARCHAR2(255),
    "Sector_Code" VARCHAR2(255),
    "Sector_Name" VARCHAR2(255),
    "Business_Unit_Code" VARCHAR2(255),
    "Business_Unit_Name" VARCHAR2(255),
    "Department_Code" VARCHAR2(255),
    "Department_Name" VARCHAR2(255),
    "HR_ORG_ID" VARCHAR2(255),
    "HR_ORG_Name" VARCHAR2(255),
    "Cost_Center_Number" VARCHAR2(255),
    " " VARCHAR2(255)
  )
  SEGMENT CREATION IMMEDIATE PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255 NOCOMPRESS
  </code></pre>