如何按SELECT查询中两个SUM / COUNT之比进行排序？

Question

In a SELECT query as

SELECT 
category_id, 
COUNT(*) AS Total, 
SUM(IF(year=2016,1,0) AS year2016, 
SUM(IF(year=2015,1,0) AS year2015
FROM articles
GROUP BY category_id

How can I ORDER BY the ratio of year2016/year2015 ?

Answer 1

Moving the SELECT statement into a sub-query will allow you to re-use the calculated SUM aggregates. Casting to a DECIMAL will tell MySQL not to use integer division and to keep values to the right of the decimal point.

SELECT category_id, Total, year2016, year2015
FROM
  (SELECT 
    category_id, 
    COUNT(*) AS Total, 
    SUM(IF(year=2016,1,0)) AS year2016, 
    SUM(IF(year=2015,1,0)) AS year2015
  FROM articles
  GROUP BY category_id) AS t
ORDER BY CAST(year2016 AS DECIMAL(14,4)) / CAST(year2015 AS DECIMAL(14,4))