Help with nvl and to_char in query

Question

Hi, I was wondering if anyone could help me with finding the reason that the following query gives me an invalid number error:
SELECT     to_char('dd/mm/yyyy',nvl(co_modified_date,co_added_date)) as d1
FROM     co_allergies_record_upd
WHERE          co_allergies_record_upd_id IN (
SELECT co_allergies_record_upd_id
FROM     co_allergies_link_upd
WHERE     co_allergies_rec_id = 42
ORDER BY     nvl(co_modified_date,co_added_date) DESC
Specifically, it is the nvl(co_modified_date,co_added_date) which is causing the error. The co_added_date has a NOT NULL constraint, and both are date fields. What could be causing the error?

Answer 1

You have missed format and data argument places in to_char():
SELECT to_char('dd/mm/yyyy',nvl(co_modified_date,co_added_date)) as d1
FROM co_allergies_record_upd
WHERE co_allergies_record_upd_id IN (
SELECT co_allergies_record_upd_id...
SQL> select to_char('dd/mm/yyyy',sysdate) from dual;
select to_char('dd/mm/yyyy',sysdate) from dual
ERROR at line 1:
ORA-01722: invalid number
SQL> select to_char(sysdate,'dd/mm/yyyy') from dual;
TO_CHAR(SY
20/12/2006Rgds.