Get growth rate per month from transaction table - mysql

Question

I have a transaction history like this:
date
revenue
balance
2021-05-03
0
1000
2021-05-21
500
1500
2021-05-23
-250
1250
2021-06-02
-500
750
and I would like to get a result like this:
date
growth
2021-5
0.25
2021-6
-0.4
The formula is:
balance (end of month) - balance (start of month) / balance (start of month)
e.g.: 1250-1000/1000=0.25
and: 750-1250/1250=-0.4
I would very much appreciate a hint for a MYSQL query that is as simple as possible.

Answer 1

You need to pull in the balance from the previous month, if it exists. For that, you can combine lag() with conditional aggregation:
select year(date), month(date),
(-1 +
(max(case when seqnum_desc = 1 then balance end) /
max(case when seqnum_asc = 1 then coalesce(prev_balance, balance) end)
)
) as growth
from (select t.*,
row_number() over (partition by year(date), month(date) order by date) as seqnum_asc,
row_number() over (partition by year(date), month(date) order by date desc) as seqnum_desc,
lag(balance) over (order by date) as prev_balance
from t
) t
group by year(date), month(date);
Here is a db<>fiddle.

Answer 2

#MBauerDC ... Thank You. In my case this was the right direction as I work with MYSQL 5.7. However, a few changes were still necessary to get to the final result:
SELECT
t0.month,
(t2.balance - (t1.balance - t1.revenue)) / (t1.balance - t1.revenue) AS growth
FROM
(SELECT
DATE_FORMAT(date, '%Y-%m') AS 'month',
MIN(date) AS 'min_date',
MAX(date) AS 'max_date'
FROM
t
GROUP BY month) AS t0
JOIN
t AS t1 ON (t1.date = min_date)
JOIN
t AS t2 ON (t2.date = max_date)

Answer 3

The logic of this calculation isn't consistent by your example.
Let's take "start of month" and "end of month" as the record with the first date in the month and the record with the last date in the month.
By this calculation, you do arrive at "0.25" for month 05, but for month 06, there is only one record, so its both the first and last record of the month, and the calculation is (750-750)/750, which is zero.
In your example calculation, you take the end of the last month to calculate the value for month 06, but take the end and start of month 05 for the calculation of the growth in month 05. These are two different calculations! You'll have to decide which one to use.
If you want to use the first and last record in a given month (as you do for month 05), you can use this:
SELECT
`t0`.`month`,
IF(`t1`.balance = 0,
NULL,
((`t2`.balance - `t1`.balance) / `t1`.balance)) AS `growth`
FROM
(SELECT
DATE_FORMAT(`date`, '%Y-%m') AS 'month',
MIN(`date`) AS 'min_date',
MAX(`date`) AS 'max_date'
FROM
`your_table`
GROUP BY MONTH(`date`)) AS `t0`
JOIN
`your_table` AS `t1` ON (`t1`.date = `min_date`)
JOIN
`your_table` AS `t2` ON (`t2`.date = `max_date`);
Note the "IF" because you have to guard against dividing by zero - a growth from zero to any positive value is always "infinity percent", which makes no sense to use - so you have to know how the things you're trying to build should work in these cases.

Answer 4

Provided that the DB version is 8.0, then you can use analytic functions as in the following query
SELECT month,
(bal_end - COALESCE(LAG(bal_end) OVER(ORDER BY month), bal_start)) /
COALESCE(LAG(bal_end) OVER(ORDER BY month), bal_start) AS growth
FROM (SELECT month,
MAX(CASE
WHEN m_end = 1 THEN
sum_balance
END) AS bal_end,
MAX(CASE
WHEN m_start = 1 THEN
sum_balance
END) bal_start
FROM (SELECT month,
SUM(COALESCE(CASE
WHEN bal_start = 1 THEN
balance
END,
0) + COALESCE(revenue, 0)) OVER(ORDER BY date) AS sum_balance,
m_end,
m_start,
date
FROM (SELECT DATE_FORMAT(date, '%Y-%m') AS month,
t.*,
ROW_NUMBER() OVER(PARTITION BY DATE_FORMAT(date, '%Y-%m') ORDER BY date) AS m_start,
ROW_NUMBER() OVER(PARTITION BY DATE_FORMAT(date, '%Y-%m') ORDER BY date DESC) AS m_end,
ROW_NUMBER() OVER(ORDER BY date) AS bal_start
FROM t) AS t0) AS t1
GROUP BY month) AS t2;
month
growth
2021-05
0.2500
2021-06
-0.4000
Demo