title: How to add a user defined column with a single value to a SQL query
body: <p>I currently have a SQL query that produces a table with around 10M rows. I would like to append this table with another column that has the same entry for all 10M rows. </p>
  
  <p>As an example consider the following toy query</p>
  
  <pre><code>SELECT PRODUCT_ID, ORDER_QUANTITY
  FROM PRODUCT_TABLE
  GROUP BY SALES_DAY
  </code></pre>
  
  <p>And say that is produces the following table</p>
  
  <pre><code> PRODUCT_ID ORDER_QUANTITY`     
        1          10
        2          12
        3          14
  </code></pre>
  
  <p>How can I change this query so that it produces the following table, where every entry in USER_VALUE is 999.</p>
  
  <pre><code> PRODUCT_ID ORDER_QUANTITY USER_VALUE  
        1           10         999
        2           12         999
        3           14         999
  </code></pre>
  
  <p>I realize that there may be several answers here... but I suppose that it would help to know the method that would be produce the table with the smallest file size (I assume this would require specifying the type of data beforehand).</p>