title: Sum multiple columns in 2 tables
body: <p>I have two tables(sales_today and last_year_same_day_sales).  From sales_today table, I would like to sum both t_net_sales and t_gross_margin columns.
  From last_year_same_day_sales, I would like to sum both ly_net_sales and ly_gross_margin columns and display results in one table as I have shown below</p>
  
  <pre><code>sales_today
  store_number | t_net_sales | t_gross_margin
  1            | 100.00      | 20.00
  2            | 150.00      | 35.00
  
  last_year_same_day_sales
  store_number | ly_net_sales| ly_gross_margin
  1            | 175.00      | 50.00
  2            | 125.00      | 25.00
  3            | 75.00       | 10.00
  
  results
  today_net_sales | last_year_net_sales | today_gross_margin | last_year_gross_margin
  250.00          | 375.00              | 55.00              | 85.00
  </code></pre>
  
  <p>Here is my query:</p>
  
  <pre><code>SELECT
    (SELECT SUM(t_net_sales) FROM sales_today) AS today_net_sales,
    (SELECT SUM(ly_net_sales) FROM last_year_same_day_sales) AS last_year_net_sales,
    (SELECT SUM(t_gross_margin) FROM sales_today) AS today_gross_margin,
    (SELECT SUM(ly_gross_margin) FROM last_year_same_day_sales) AS last_year_gross_margin
  </code></pre>
  
  <p>I get the proper results with the query. Is there a better way?</p>