Database date depending on SYSDATE with a condition - sql

Question

I would like to select and return a number of rows depending on 'today's' date.
Something like...
SELECT * FROM my_table
WHERE
//some conditions AND
my_DATE BETWEEN trunc (sysdate, 'mm')/*current month*/ AND SYSDATE
However I would like to return:
Only rows for the last two months (excluding this month) if today's date 'dd' is less than 15
Return rows for the last two months (including this month) if today's date is >= 15
I am thinking of a case. Something like
WHERE
(CASE
when trunc (sysdate, 'dd') < 15 THEN
TO_CHAR(my_DATE, 'MMYYY') BETWEEN TO_CHAR((add_months(sysdate,-3)) AND TO_CHAR((add_months(sysdate,-1))
Any pointers are highly appreciated as I get acquainted with this arena. Thank you

Answer 1

I would do all the computation on sysdate, to help the optimizer user indexes:
where datecol >= add_months(trunc(sysdate, 'MON'),
(case when extract(day from sysdate) < 15 then -2 else -1 end)
) and
datecol < add_months(trunc(sysdate, 'MON'),
(case when extract(day from sysdate) < 15 then 0 else 1 end)
)
EDIT:
Based on the comment:
where datecol >= add_months(trunc(sysdate, 'MON'), -2) and
datecol < add_months(trunc(sysdate, 'MON'),
(case when extract(day from sysdate) < 15 then 0 else 1 end)
)

Answer 2

If this represents sample data:
SQL> alter session set nls_date_format = 'dd.mm.yyyy';
Session altered.
SQL> select * from test order by id;
ID DATUM
---------- ----------
1 20.12.2020
2 07.01.2021
3 15.02.2021
4 25.02.2021
5 10.03.2021
then see whether the following code makes sense. The whole date '&&par_sysdate' shuld be replaced by sysdate in real life; for testing purposes, I used a parameter as sysdate returns today's date.
First example: par_sysdate = 10.03.2021 (day is less than 15):
SQL> select t.id, t.datum
2 from test t
3 where t.datum >=
4 trunc(add_months(date '&&par_sysdate',
5 -case when to_number(to_char(date '&&par_sysdate', 'dd')) < 15 then 2
6 else 1
7 end
8 ), 'mm')
9 and t.datum < case when to_number(to_char(date '&&par_sysdate', 'dd')) < 15 then
10 trunc(date '&&par_sysdate', 'mm')
11 else date '&&par_sysdate'
12 end;
Enter value for par_sysdate: 2021-03-10
ID DATUM
---------- ----------
2 07.01.2021
3 15.02.2021
4 25.02.2021
Second example: using today's date (20.03.2021) where day is greater than 15:
SQL> undefine par_sysdate
SQL> /
Enter value for par_sysdate: 2021-03-20
ID DATUM
---------- ----------
3 15.02.2021
4 25.02.2021
5 10.03.2021
SQL>
Or, as I said, using sysdate:
SQL> select t.id, t.datum
2 from test t
3 where t.datum >=
4 trunc(add_months(sysdate,
5 -case when to_number(to_char(sysdate, 'dd')) < 15 then 2
6 else 1
7 end
8 ), 'mm')
9 and t.datum < case when to_number(to_char(sysdate, 'dd')) < 15 then
10 trunc(sysdate, 'mm')
11 else sysdate
12 end;
ID DATUM
---------- ----------
3 15.02.2021
4 25.02.2021
5 10.03.2021
SQL>

Answer 3

Your requirements are not wholly clear, but I think you want something like this:
select t.*
from mytable t
where (to_number(to_char(sysdate, 'dd')) < 15
and t.dt >= add_months(trunc(sysdate, 'mm'),-3)
and t.dt < trunc(sysdate, 'mm')
)
or (to_number(to_char(sysdate, 'dd')) >= 15
and t.dt >= add_months(trunc(sysdate, 'mm'),-2)
and t.dt <= last_day(sysdate)
)
I have put a demo version of this code on db<>fiddle with an affordance for changing the date of today instead of using sysdate.
the previous months should be FULL not previous months based on today's date.
To get full months, truncate the date using the 'mm' mask, which returns the first of the month.