Getting the Sunday dates using Next_Day

Question

The requirement is:
Get the Sunday of this week and Sunday of the last week. As system date is 02-July, this Sunday is 01-July and last week Sunday is 24-Jun. If say suppose the system date is 01-July, then this Sunday should be 24-Jun and last Sunday should be 17-Jun. I tried something like :
Select
Next_Day(sysdate-8,'SUNDAY') sunday,
Next_Day(sysdate,'SUNDAY') End_Sunday,
To_Char(Next_Day(sysdate-8,'SUNDAY'),'YYYYMMDD') sun_mm,
1 Fl
From
Dual
Union
Select
Next_Day(sysdate-16,'SUNDAY') sunday,
Next_Day(sysdate-16,'SUNDAY')+7 End_Sunday,
To_Char(Next_Day(sysdate-16,'SUNDAY'),'YYYYMMDD') sun_mm,
2 Fl
From
Dual
I know the above doesn't work due to -16. Need some help in meeting the requirement.
Thanks
Chaitanya.S.S.K

Answer 1

Micheals,
this?
SQL> alter session set nls_territory=germany;
Session altered.
SQL>  WITH t AS  ( SELECT SYSDATE AS DT FROM dual
  2               UNION ALL
  3       SELECT TO_DATE('07/01/2007','MM/DD/YYYY') FROM dual
  4         UNION ALL
  5       SELECT TO_DATE('07/02/2007','MM/DD/YYYY') FROM dual
  6       UNION ALL
  7       SELECT TO_DATE('06/30/2007','MM/DD/YYYY') FROM dual)
  8   SELECT DT, CASE WHEN TO_CHAR(DT,'DY')='SUN' THEN
  9                       TRUNC(dt,'d')-7
10       ELSE 
11           TRUNC(dt,'d')
12       END last_sunday
13   FROM  t;
DT       LAST_SUN
03.07.07 02.07.07
01.07.07 18.06.07
02.07.07 02.07.07
30.06.07 25.06.07
SQL> alter session set nls_territory=america;
Session altered.
SQL>  WITH t AS  ( SELECT SYSDATE AS DT FROM dual
  2               UNION ALL
  3       SELECT TO_DATE('07/01/2007','MM/DD/YYYY') FROM dual
  4         UNION ALL
  5       SELECT TO_DATE('07/02/2007','MM/DD/YYYY') FROM dual
  6       UNION ALL
  7       SELECT TO_DATE('06/30/2007','MM/DD/YYYY') FROM dual)
  8   SELECT DT, CASE WHEN TO_CHAR(DT,'DY')='SUN' THEN
  9                       TRUNC(dt,'d')-7
10       ELSE 
11           TRUNC(dt,'d')
12       END last_sunday
13   FROM  t;
DT        LAST_SUND
03-JUL-07 01-JUL-07
01-JUL-07 24-JUN-07
02-JUL-07 01-JUL-07
30-JUN-07 24-JUN-07