SQL query for incoming and outgoing stocks, first and last - sql

Question

I need to make a query that shows sales and stocks (incoming and outgoing) for each model in October 2021.
The point is that for obtaining incoming and outgoing stocks I need to get vt_stocks_cube_sz.qty respectively for the first day of month and for the last day of month .
Now I wrote just sum of stocks (SUM(vt_stocks_cube_sz.qty) as stocks) but it isn't correct.
Could you help me to split the stocks according to the rule above, I cannot understant how to write the query correctly.
%%time
SELECT vt_sales_cube_sz.modc_barc2 model,
SUM(vt_sales_cube_sz.qnt) sales,
SUM(vt_stocks_cube_sz.qty) as stocks
FROM vt_sales_cube_sz
LEFT JOIN vt_date_cube2
ON vt_sales_cube_sz.id_calendar_int = vt_date_cube2.id_calendar_int
LEFT JOIN vt_stocks_cube_sz ON
vt_stocks_cube_sz.parent_modc_barc = vt_sales_cube_sz.modc_barc AND
vt_stocks_cube_sz.id_stock = vt_sales_cube_sz.id_stock AND
vt_stocks_cube_sz.id_calendar_int = vt_sales_cube_sz.id_calendar_int AND
vt_stocks_cube_sz.vipusk_type = vt_sales_cube_sz.price_type
WHERE vt_date_cube2.wk_year_id = 2021
AND vt_date_cube2.wk_MoY_id = 10
AND vt_sales_cube_sz.id_stock IN
(SELECT id_stock
FROM vt_warehouse_cube
WHERE channel = \'OffLine\')
GROUP BY vt_sales_cube_sz.modc_barc2

Answer 1

If you're looking for a robust and generalizable approach I'd suggest using analytic functions such as FIRST_VALUE, LAST_VALUE or something slightly different with RANK or ROW_NUMBER.
A simple example follows, so you can rerun it on your side and adjust it to the specific tables/fields you're using.
N.B.: You might need some tiebreakers in case you had multiple entries for the same first/last day.
with dummy_table as (
SELECT 1 as month, 1 as day, 10 as value UNION ALL
SELECT 1 as month, 2 as day, 20 as value UNION ALL
SELECT 1 as month, 3 as day, 30 as value UNION ALL
SELECT 2 as month, 1 as day, 5 as value UNION ALL
SELECT 2 as month, 3 as day, 15 as value UNION ALL
SELECT 2 as month, 5 as day, 25 as value
)
SELECT
month,
day,
case when day = first_day then 'first' else 'last' end as type,
value,
FROM (
SELECT *
, FIRST_VALUE(day) over (partition by month order by day ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) as first_day
, LAST_VALUE(day) over (partition by month order by day ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) as last_day
FROM dummy_table
) tmp
WHERE day = first_day OR day=last_day
Dummy table:
Row
month
day
value
1
1
1
10
2
1
2
20
3
1
3
30
4
2
1
5
5
2
3
15
6
2
5
25
Result:
Row
month
day
type
value
1
1
1
first
10
2
1
3
last
30
3
2
1
first
5
4
2
5
last
25