Oracle sql sort week days by current day - sql

Question

I am trying to sort the days based on the order: Saturday, Sunday, Monday, Tuesday, Wednesday, Thursday, Friday.
I am trying using case:
select day,
CASE day
WHEN 1 THEN 1
WHEN 2 THEN 2
WHEN 3 THEN 3
WHEN 4 THEN 4
WHEN 5 THEN 5
WHEN 6 THEN 6
WHEN 7 THEN 7
else 0
END as day_nr
from week where day in (1,2,3,4,5,6,7)
order by day_nr asc
This is ok when I select all the days of the week. But if I want only for the day 1,5,6 the ordering is not correct. Gets the first day -Monday. How to proceed?

Answer 1

If you're trying to sort a set of dates by day of the week, with Saturday being the first, then consider ordering by a modified date:
create table t1(my_date date);
insert into t1
select trunc(sysdate)+rownum
from dual
connect by level <= 20
select
my_date,
to_char(my_date,'Day'),
to_char(my_date,'D')
from
t1
order by
to_char(my_date + 1,'D');
http://sqlfiddle.com/#!4/5940b/3
The downside is that it's not very intuitive, so add a code comment if you use this method.
Edit: Where you have a list of numbers, order by a case statement with either a list conversion:
case day
when 1 then 3
when 2 then 4
when 3 then 5
when 4 then 6
when 5 then 7
when 6 then 1 -- saturday
when 7 then 2
end
... or the more compact, but not as intuitive:
case
when day <= 5 then day + 2
else day - 5
end
order by case

Answer 2

In Oracle day 1 is Sunday by default.
SELECT * FROM
(
SELECT trunc(sysdate) + LEVEL-1 my_dt
, TO_CHAR(trunc(sysdate) + LEVEL-1, 'DY') Wk_Day
, TO_CHAR(trunc(sysdate) + LEVEL-2, 'D' ) Day#
FROM dual
CONNECT BY LEVEL <= 10
)
WHERE Day# IN (1,5,6)
ORDER BY my_dt, Day#
/
MY_DT WK_DAY DAY#
------------------------
5/10/2013 FRI 5
5/11/2013 SAT 6
5/13/2013 MON 1
5/17/2013 FRI 5
5/18/2013 SAT 6