Question

I’m trying to calculate a percentage in my SQL query.

This is what I have right now:

SELECT
DATE(processed_at) AS day,
(
  SELECT
  COUNT(*) FROM return_items
  WHERE return_id IN (SELECT id FROM returns WHERE DATE(processed_at) = day)
) as products_returned,
COUNT(*) as return_count,
(
  SELECT
  COUNT(*) as co_returns
  FROM returns
  WHERE return_method = 'mondial_relais'
  AND DATE(processed_at) = day
) as return_rate_mr
FROM returns
WHERE MONTH(processed_at) = 10
AND YEAR(processed_at) = 2011
GROUP BY day;

Basically I need the return_rate_mr to be a percentage value.
I tried doing something like return_rate_mr * 100 / return_count as perc_value but this doesn’t work. (I don’t actually need the current return_rate_mr value, just the percentage.

Any ideas?

Answer 1

Assuming your original query returns the desired results, you can wrap it as a subquery:

SELECT
    day,
    return_rate_mr * 100 / return_count as perc_value,
    ... any other columns ...
FROM
    ( ... your original query here ...) as myalias;

Basically, the subquery creates a result set where the columns are renamed. Then, the outer query is free to use those new column names.