Sql query to_date function

Question

hi all,
I am working on a project where some sql scripts are already been developed by
someone else.
In the code i found
Select col_name
from table_name
where txn_dt between to_date(to_date('05-dec-2007') - 6) and to_date('05-dec-2007');
I am wondering whats the usage of 2 to_date function in the where clause.
This can be achieved using this as well:
Select col_name
from table_name
where txn_dt between to_date('05-dec-2007') - 6 and to_date('05-dec-2007');
Can anybody tell me this diff if there is any?
Thanks
Shane

Answer 1

to_date(to_date('05-dec-2007') - 6)This is an error. Not a syntax error, but a runtime error waiting to happen.
The inner to_date is fine (except it should have a format mask) but the outer to_date is expecting a character type and it's getting a date. So it has to be converted.
All this depends on the nls settings which could change.
Ideally, the code should read:
Select col_name
from table_name
where txn_dt between to_date('05-dec-2007','dd-mon-yyyy') - 6 and to_date('05-dec-2007','dd-mon-yyyy');
(on second thought...if the nls settings match this date format, it should convert without error in both to_date functions, but still...why do it?)
Edited by: SomeoneElse on Dec 12, 2008 9:12 AM