title: SUM with group by return error
body: <p>Having this two table</p>
  
  <p>DEPARTMENT</p>
  
  <pre><code>//DEPARTMENT
  D#          DNAME
  -------------------
  1         RESEARCH
  2            IT
  3          SCIENCE
  </code></pre>
  
  <p>PROJECT</p>
  
  <pre><code>//PROJECT
  P#       D#        BUDGET
  -------------------------
  1001     1         22500
  1002     1         22500
  1003     3         50000
  </code></pre>
  
  <p>When i execute this command</p>
  
  <pre><code>SELECT d.D#,DNAME,sum(budget) as "TOTAL BUDGETS" 
      FROM DEPARTMENT d,PROJECT p 
  WHERE d.D# = p.D#
  GROUP BY d.D#;
  </code></pre>
  
  <p>I thought result will be </p>
  
  <pre><code>D#     DNAME     TOTAL BUDGETS
  ------------------------------
  1     RESEARCH       45000
  2        IT             0
  3       SCIENCE      50000
  </code></pre>
  
  <p>but why i get this error</p>
  
  <pre><code>//Oracle: NOT A GROUP BY EXPRESSION ERROR
  </code></pre>