title: TSQL - Average of all values in a column that are not zero
body: <p>I'm in the process of writing a report and am looking to get the average value of an age column. The problem is that not all rows have an age.</p>
  
  <p>If the values for the column are 0 2 4 I would want 3 returned, not 2. I can not simply exclude the zero rows with a WHERE as I'm using using other columns in those rows. Is there such a thing as a AvgIfNotZero type of function?</p>