Previous Saturday's date

Question

I need to write a function that will return the previous Saturday's date from a date passed into the function.
On a similar note I need to be able to get Friday's date of 4 weeks from a specific date passed into the function.
Thank you in advance for answering this post and any help will be appreciated.
Thanks
Adam

Answer 1

"APCs solution has the drawback that you need to provide the weekday in the date language of your session"
An easy workaround if you don't know the date language for the session:
last Saturday
SQL> SELECT NEXT_DAY(sysdate-7, TO_CHAR(TO_DATE('03-jan-1970','dd-mon-yyyy', 'nls_date_language = ENGLISH'), 'DAY'))
  2  FROM dual;
NEXT_DAY(
22-APR-06Friday 4 weeks off:
SQL> SELECT NEXT_DAY(sysdate+28, TO_CHAR(TO_DATE('02-jan-1970','dd-mon-yyyy', 'nls_date_language = ENGLISH'), 'DAY'))
  2  FROM dual;
NEXT_DAY(
26-MAY-06Just pick a date you know is the correct day of the week.
SQL> ALTER SESSION SET nls_date_language = 'FRENCH';
Session altered.
SQL> SELECT NEXT_DAY(sysdate-7, TO_CHAR(TO_DATE('03-jan-1970','dd-mon-yyyy', 'nls_date_language = ENGLISH'), 'DAY'))
  2  from dual;
NEXT_DAY(
22-AVR-06Voila, language independent.
The nls_date_language parameter is required in the TO_DATE to avoid
SELECT TO_DATE('22-apr-2006','dd-mon-yyyy') from dual;
SELECT TO_DATE('22-apr-2006','dd-mon-yyyy') from dual
ERROR at line 1:
ORA-01843: not a valid monthWhen the date language is different.
TTFN
John