title: SQL LEFT JOIN using alias name
body: <p>Just started working on Oracle SQL and trying to use left join. Getting following error, plz help. </p>
  
  <pre><code>select usr_grpid as "usr_role_role_id" 
  from users 
  left join user_role on users.usr_role_role_id = user_role.usr_role_role_id;
  </code></pre>
  
  <p>Error Message: </p>
  
  <blockquote>
    <p>ORA-00904: "USERS"."USR_ROLE_ROLE_ID": invalid identifier
    00904. 00000 -  "%s: invalid identifier"</p>
  </blockquote>
  
  <p>Actually column name of first table is different then second table though the data is same.</p>