title: inner join with group by expression in oracle sql
body: <p>I am new to sql, any help is appreciated.</p>
  
  <p>I have two tables, <code>employees</code> and <code>jobs</code>. <code>employees</code> contain a variable <code>job_id</code> (multiple employees can have the same job_ID). <code>jobs</code> contain variables <code>job_id</code> and <code>job_title</code> (one job_ID correspond to one job_title, this is the hr schema in oracle if you are interested).</p>
  
  <p>I want the query to return: the job_title, job_ID and the number of people who have the same job_Id.</p>
  
  <p>I tried the following code:</p>
  
  <pre><code>select j.job_title, e.job_ID, count(e.job_ID)
  from employees e, jobs j
  where e.job_id=j.job_id
  group by e.job_Id
  </code></pre>
  
  <p>the error message is:</p>
  
  <blockquote>
    <p>ORA-00979: not a GROUP BY expression
    00979. 00000 -  "not a GROUP BY expression"
    *Cause:<br>
    *Action:<br>
    Error at Line: 83 Column: 8</p>
  </blockquote>
  
  <p>Can you help me fix this?</p>