Removing the data portion

Question

Hi ,
I have a varchar2 field that stores time :
16:29:00
08:30:00...
i want to query this column but after converting it to date and getting only the time portion so i can make some comparisons , but when i issue this query the date part still shows :
select TO_DATE(ACTION_TIME,'HH24:MI:SS')
FROM V$EVENTLOGS;i also tried this select TO_DATE(to_char(ACTION_TIME,'HH24:MI:SS'),'HH24:MI:SS')
FROM V$EVENTLOGS;but it gives:
ERROR at line 1:
ORA-01722: invalid number
Thanks

Answer 1

Hi,
oais wrote:
select TO_DATE(ACTION_TIME,'HH24:MI:SS')
FROM V$EVENTLOGS;i also tried this select TO_DATE(to_char(ACTION_TIME,'HH24:MI:SS'),'HH24:MI:SS')
FROM V$EVENTLOGS;but it gives:
ERROR at line 1:
ORA-01722: invalid numberPerhaps it really means that.
If even one of the strings contains something other than a number (e.g. '??:00:00', you will get that error, and no other results.
To see what rows are not in the correct format, use TRANSLATE.
SELECT  action_time
FROM     v$event_logs     -- as others have said, a confusing name
WHERE     TRANSLATE ( action_time
            , '123456789'
            , '000000000'
            ) != '00:00:00'
;you'll get a different error message if the string contains a valid number that does not happen to be a valid hour, minute or second. You might as well check for those errors at the same time:
SELECT  action_time
FROM     v$event_logs     -- as others have said, a confusing name
WHERE     TRANSLATE ( action_time
            , '123456789'
            , '000000000'
            ) != '00:00:00'
OR     SUBSTR (action_time, 1, 2)     NOT BETWEEN '00' AND '23'
OR     SUBSTR (action_time, 4, 2)     NOT BETWEEN '00' AND '59'
OR     SUBSTR (action_time, 7, 2)     NOT BETWEEN '00' AND '59'
;You should correct (or remove) the invalid strings from the table, then add a CHECK constraint to make sure the data stays clean.
Why are you converting the strings to a DATE?
If you just need to display them, or compare them (e.g., find times between '08:00:00' and '18:00:00') it's better to leave them as strings.
If you do convert them using TO_DATE, note what Justin said:
An Oracle date always has a day component and a time component. If you convert the string '16:29:00' to a date, that automatically becomes today (i.e. 18 April 2009) at 16:29:00.I think Justin made a typo, though. If you don't give a day of the month in TO_DATE, it defaults to the 1st of the month, not the current day.
That is
TO_DATE ( '16:29:00'
        , 'HH24:MI:SS'
        )returns 01-Apr-2009 16:29:40 when run today (April 18) or any time during April 2009.