Calculating month over month numbers - mysql

Question

I searched around and found solutions, but they didn't work with MySQL because they used functions from other software.
I'm trying to show month-over-month growth for the current year (starting January), though knowing how to check within the past year might come in handy in the future as well.
What the "orders" table might look like:
+-----------+-------+
| Month | Sales |
+-----------+-------+
| 1-1-2017 | 3 |
| 1-5-2017 | 9 |
| 2-16-2017 | 10 |
| 2-16-2017 | 13 |
| 3-7-2017 | 25 |
| 4-29-2017 | 22 |
+-----------+-------+
What I want the query result to look like:
+----------+-------+--------+
| Month | Sales | Growth |
+----------+-------+--------+
| January | 12 | |
| February | 23 | 91.66% |
| March | 25 | 8.69% |
| April | 22 | -12% |
+----------+-------+--------+
Is there a simple way to do this?

Answer 1

You can do something like that:
SELECT
thisMonth.MonthOnly,
SUM(thisMonth.Sales) AS ThisMonthSales,
(SUM(thisMonth.Sales) / SUM(lastMonth.Sales) - 1) * 100 AS Growth
FROM
(
SELECT STR_TO_DATE(DATE_FORMAT(Month, '%Y%m01'), '%Y%m%d') AS MonthOnly,
SUM(Sales) AS Sales
FROM orders
GROUP BY DATE_FORMAT(Month, '%Y%m01')
) thisMonth
LEFT OUTER JOIN
(
SELECT STR_TO_DATE(DATE_FORMAT(DATE_ADD(Month, INTERVAL 1 MONTH), '%Y%m01'), '%Y%m%d') AS MonthOnly,
SUM(Sales) AS Sales
FROM orders
GROUP BY DATE_FORMAT(Month, '%Y%m01')
) lastMonth
ON thisMonth.MonthOnly = lastMonth.MonthOnly
GROUP BY thisMonth.MonthOnly