Format Date question as VARCHAR

Question

Using Oracle 10g:
I have a varchar field that is holding a date like:
2010-08-28 14:40:21
I'm trying to format the date so I can check if it's greater than the sysdate. I'm trying to do:
TO_CHAR(end_date, 'YYYYMMDD' ) > to_char(sysdate,'YYYYMMDD');
I'm getting an error:
ORA-01722: invalid number
01722. 00000 - "invalid number"
Which makes sense but I'm just not sure how to properly format the end_date to the YYYYMMDD format.

Answer 1

Hi,
user9179751 wrote:
Using Oracle 10g:
I have a varchar field that is holding a date like:
2010-08-28 14:40:21
I'm trying to format the date so I can check if it's greater than the sysdate. I'm trying to do:
TO_CHAR(end_date, 'YYYYMMDD' ) > to_char(sysdate,'YYYYMMDD');
I'm getting an error:
ORA-01722: invalid number
01722. 00000 - "invalid number"
Which makes sense but I'm just not sure how to properly format the end_date to the YYYYMMDD format.Is end_date the VARCHAR2 column?
TO_CHAR, as the name suggests, converts a DATE TO a <b>CHAR</b>acter string. If you already have a character string, then there's no need for TO_CHAR.
You might want to call TO_DATE, such as
WHERE   TO_DATE ( end_date
                , 'YYYY-MM-DD HH24:MI:SS'
                )  > SYSDATEbut it's more efficient and less error prone to say
WHERE   end_date > TO_CHAR (SYSDATE, 'YYYY-MM-DD HH24:MI:SS')Why is it more efficient? The optimizer considers SYSDATE to be a constant, even if the query takes a significant amount of time. Therefore, it will only convert SYSDATE into a string once, even if you have a million rows in the table. If you did it the first way, you would have to call TO_DATE a million times, once for each row. Also, because your column, end_date, is alone on one side of the > operator, the optimizer can use an index on that column.
Why is it less error prone? If you have even one row where end_date is malformed, you'll get an error if you call TO_DATE. By not even trying to convert end_date, you don't risk any errors.
This only works because the format of end_date is suitable for sorting. If the format were, say, 'DD-Mon-YYYY', you would have to convert it to a DATE.
It would be better if end_date were a DATE column. It's never a good idea to use a VARCHAR2 column to store points in time.