SQL script to show current week and first week of every month - sql

Question

I have written sql code to pull all the data that I need but the startdate is in weeks. I need to see the current week and then for future dates I need to see the first date of each month. (Like I said these are in weeks and the date is each Monday. (ex. 03-JUN-19, 10-JUN-19, 17-JUN-19....)
select
d.ITEM,
i.DESCRIPTION,
d.MARKET,
(CASE
WHEN d.LOC like 'U%' THEN 'US'
WHEN d.LOC like 'M%' THEN 'MX'
WHEN d.LOC like 'C%' THEN 'CA'
ELSE 'EXP' END) as COUNTRY,
d.START_DATE as STARTDATE,
SUM(d.DEMANDQTY) as QTY
from DEMAND d, ITEM i
where d.ITEM = i.ITEM
GROUP BY d.ITEM, i.DESCRIPTION, d.MARKET, d.LOC,d.START_DATE
So if I pulled this data today (7-JUN-19) I would need to only pull dates that are...03-JUN-19, 01-JUL-19, 05-AUG-19, 02-SEP-19, 07-OCT-19, 04-NOV-19, 02-DEC-19, 06-JAN-20 on and on until the data is done.

Answer 1

You need a calendar which will return desired dates - the first Monday (that follows today), and then the first Monday in every month. Here's how:
SQL> with
2 this_year as
3 (select trunc(sysdate) + level - 1 datum
4 from dual
5 connect by level <= date '2019-12-31' - trunc(sysdate) + 1
6 ),
7 formatted as
8 (select datum,
9 to_char(datum, 'd') day_num,
10 to_char(datum, 'dy', 'nls_date_language = english') day_name
11 from this_year
12 )
13 select *
14 from formatted f
15 where 1 = 1
16 and f.datum = (select min(f1.datum)
17 from formatted f1
18 where f1.day_num = 1
19 and to_char(f1.datum, 'yyyymm') = to_char(f.datum, 'yyyymm')
20 );
DATUM D DAY_NAME
---------- - ------------
10.06.2019 1 mon
01.07.2019 1 mon
05.08.2019 1 mon
02.09.2019 1 mon
07.10.2019 1 mon
04.11.2019 1 mon
02.12.2019 1 mon
7 rows selected.
SQL>
What does it do?
this_year CTE returns all dates from "today" to Dec 31st 2019. If there's some MAX date you can use - use it
formatted CTE is an intermediate step; if you run it, you'll see that day_num represents ordinal number of a day (1, 2, ... 7), while day_name returns their abbreviate names (mon, tue, ...). We are interested in day number 1 as it represents Mondays
the final select returns desired result - the first Monday in every month
Once you have those dates, use them in your current query. How? A simple option is to create a view based on such a query, e.g.
SQL> create or replace view v_mondays as
2 with
3 this_year as ...
<snip>
View created.
SQL> select * From v_mondays;
DATUM D DAY_NAME
---------- - ------------
10.06.2019 1 mon
01.07.2019 1 mon
<snip>
7 rows selected.
SQL>
Expanded, your query might look like this:
select
d.item,
i.description,
d.market,
case
when d.loc like 'U%' then 'US'
when d.loc like 'M%' then 'MX'
when d.loc like 'C%' then 'CA'
else 'EXP'
end as country,
d.start_date as startdate,
sum(d.demandqty) as qty
from demand d join item i on d.item = i.item
join v_mondays m on m.datum = d.start_date --> join with Mondays
group by d.item, i.description, d.market, d.loc,d.start_date;