title: Need a column to auto increment based on another with trigger
body: <p>I have a simple table. It has 5 columns, two of which are <code>job_num</code> and <code>line</code>.  I would like to leave the line number blank on insert and possibly use a trigger to insert a "1" if there are no other lines with that job number.  If there is a <code>job_num</code> already with a line then it would take the next line number.</p>
  
  <p>These are my columns</p>
  
  <pre><code>`job_Num` int,
  `line` int ,
  `Description` nvarchar(60),
  `qty` int,
  `price` int
  </code></pre>