How to get data by end date of every month of year? - php

Question

This is sample data in my table
id_item | qty | t_in | t_out | created_at
1 5 1 0 2018-07-05 10:41:00
1 5 1 0 2018-08-03 10:41:00
1 5 0 1 2018-08-05 10:41:00
1 5 1 0 2018-09-05 10:41:00
1 5 1 0 2018-09-20 10:41:00
1 5 0 1 2018-10-31 10:41:00
My expected result will be
id_item | qty | year | month
1 5 2018 07
1 5 2018 08
1 15 2018 09
1 10 2018 10
What i have tried it works, but not desired output when want to group by montly
$date = '2018-10-31'
$test = Model::whereDate('created_at','<=',$date)->select(DB::raw('(SUM(CASE T_IN WHEN 1 THEN qty ELSE qty * - 1 END)) as total'))->groupBy('id_item')->get();
Raw queries to get the quantity for one month
Select id_item,
(SUM(CASE T_IN WHEN 1 THEN qty ELSE qty * - 1 END)) as total
from transactions
where DATE(created_at) <= 2018-10-31
group by id_item
Worst case
$last_day_of_month = [//list of last day of each month]
//then using loop to get qty of each month refer to the raw queries above
From the query above, i only able to get one line of record. I also tried to group by month and year but incorrect result caused of the date condition. How can i include multiple <= $date condition and group it accordingly to get desired output?
Any idea or is that possible to make it? Thanks.

Answer 1

It is a Rolling Sum problem. In newer versions of Mariadb/MySQL, it can be solved using Window Functions with Frames. However, you don't have that available.
We can rather solve this using user-defined variables. In a Derived table, we first determine the total change in qty for a month. Then, we use this result-set to calculate "final qty" at the end of a month, by adding up the previous month (row)'s qty with current month (row)'s qty_change.
I have also extended the query to consider the cases when there are more than one id_item values.
Try the following Raw query:
SELECT
#roll_qty := CASE WHEN #id_itm = dt.id_item
THEN #roll_qty + dt.qty_change
ELSE dt.qty_change
END AS qty,
#id_itm := dt.id_item AS id_item,
dt.year,
dt.month
FROM
(
SELECT
t.id_item,
SUM(t.qty * t.t_in - t.qty * t.t_out) AS qty_change,
YEAR(t.created_at) AS `year`,
LPAD(MONTH(t.created_at), 2, '0') AS `month`
FROM your_table AS t
GROUP BY t.id_item, `year`, `month`
ORDER BY t.id_item, `year`, `month`
) AS dt
CROSS JOIN (SELECT #roll_qty := 0,
#id_itm := 0
) AS user_init_vars;
| id_item | year | month | qty |
| ------- | ---- | ----- | --- |
| 1 | 2018 | 07 | 5 |
| 1 | 2018 | 08 | 5 |
| 1 | 2018 | 09 | 15 |
| 1 | 2018 | 10 | 10 |
View on DB Fiddle

Answer 2

If you are going to use variables, you need to do it correctly. MySQL does not guarantee the order of evaluation of expressions in a SELECT. So, a variable should not be assigned in one expression and then used in another.
This makes for complicated expressions, but it is possible:
select yyyy, mm, total,
(#t := if(#ym = concat_ws('-', yyyy, mm), #t + total,
#ym := concat_ws('-', yyyy, mm), total
)
) as running_total
from (select year(created_at) as yyyy, month(created_at) as mm,
id_item,
sum(case T_IN when 1 then qty else - qty end) as total
from transactions
where created_at < '2018-11-01'
group by id_item
order by id_item, min(created_at)
) i cross join
(select #ym := '', #n := 0);