SQL: Getting the values of all weekdays of a certain calendar week - sql

Question

I am trying to get the value of bought items of all weekdays of a certain calendar week.
select to_char(angelegt_am, 'Day') angelegt_am,
sum(menge) menge
from fadorders_out
group by to_char(angelegt_am, 'Day');
this Query is giving me all values of the year but i don't know how to change it so i get the data from a certain single week.

Answer 1

Solutions like
where to_char(angelegt_am,'IW') = 44
group by to_char(angelegt_am, 'Day')
have a problem, they return grouped values from all years, not only the current year.
One solution could be this one:
select to_char(angelegt_am, 'Day') angelegt_am,
sum(menge) menge
from fadorders_out
where to_char(angelegt_am, 'IYYY-"W"IW') = '2020-W44'
group by to_char(angelegt_am, 'Day')
Getting the date from a Week (according to ISO-8601) is not trivial, for example 2021-01-04 is Week 53 of year 2020. The year from ISO-Week can be different to the actual year.
For proper conversion I use these functions:
CREATE OR REPLACE FUNCTION ISOWeek2Date(YEAR INTEGER, WEEK INTEGER) RETURN DATE DETERMINISTIC IS
res DATE;
BEGIN
IF WEEK > 53 OR WEEK < 1 THEN
RAISE VALUE_ERROR;
END IF;
res := NEXT_DAY(TO_DATE( YEAR || '0104', 'YYYYMMDD' ) - 7, 'MONDAY') + ( WEEK - 1 ) * 7;
IF TO_CHAR(res, 'fmIYYY') = YEAR THEN
RETURN res;
ELSE
RAISE VALUE_ERROR;
END IF;
END ISOWeek2Date;
CREATE OR REPLACE FUNCTION ISOWeek2Date(WEEK VARCHAR2) RETURN DATE DETERMINISTIC IS
BEGIN
IF NOT REGEXP_LIKE(WEEK, '^\d{4}-?W\d{2}$') THEN
RAISE VALUE_ERROR;
END IF;
RETURN ISOWeek2Date(REGEXP_SUBSTR(WEEK, '^\d{4}'), REGEXP_SUBSTR(WEEK, '\d{2}$'));
END ISOWeek2Date;

Answer 2

Actually you can extract week number from date and then filter using it:
select to_char(angelegt_am, 'Day') angelegt_am,
sum(menge) menge
from fadorders_out
where to_char(angelegt_am, 'iw') = 2 -- specify your week number here
group by to_char(angelegt_am, 'Day')
But please check that you and your DB have the same view on weeks start and end dates
You can further read https://docs.oracle.com/cd/B19306_01/server.102/b14200/sql_elements004.htm#i34510
Here you can find all other format arguments accepted by to_char function under the "Datetime Format Models" topic

Answer 3

Filter the data in your where clause, e.g.:
select to_char(angelegt_am, 'Day') angelegt_am,
sum(menge) menge
from fadorders_out
where angelegt_am >= to_date ( :week_start_date, 'yyyy-mm-dd' ) -- change format as appropriate
and angelegt_am < to_date ( :week_start_date, 'yyyy-mm-dd' ) + 7
group by to_char(angelegt_am, 'Day')