In oracle SQL, how would you obtain the timestamp representing the start of the week?

Question

I'm using an Oracle 9i database and want to obtain, within a function, the timestamp representing the start of the week, i.e. The most recent monday, at 00:00:00.

I am aware that the timestamp representing the start of the current day is TO_TIMESTAMP(SYSDATE).

Answer 1

You can use the function next_day to get that:

SQL> select next_day(sysdate-7, 'MONDAY') FROM DUAL;

NEXT_DAY
---------
29-APR-13

Answer 2

Getting the start of the week should work with trunc (see docs).

So,

select to_timestamp(trunc(sysdate, 'D')) from dual

should work.

However, depending on your NLS settings, the first day of the week for oracle may well be Sunday.

Answer 3

this appears to return Monday before the day of week in question at midnight. to prove out just play around with sysdate and subtract days...

select case when to_Char(sysdate,'d') = 1 then
 trunc(sysdate-6)
else 
  trunc(sysdate - (to_Char(sysdate,'d')-2))
END
  from dual;

Answer 4

You can truncate a date to Monday with:

select trunc(sysdate, 'IW') FROM DUAL;