Update Oracle timestamp to current date

Question

I have a TIMESTAMP(6) field in Oracle db. Value of this field is in format

DD/MM/YYYY HH:MM:SS.000000000 PM

How to update this value to the current timestamp?

[a link to a similar question:] update date value in oracle

I followed this link, but following query is taking very long time to execute.

update table_name set start_time = to_char(to_date(start_time, 'yyyy/mm/dd-hh:mi:ss:ff3'), '2012/10/10-19:30:00:00') where column='Q'

Answer 1

A timestamp is a point in time, it has no format. To update such a field to the current timestamp, use SYSTIMESTAMP or CURRENT_TIMESTAMP (respectively the date/time of the server and the date/time of the session):

UPDATE your_table 
   SET your_column = systimestamp
 WHERE ...

If the query takes an abnormal amount of time (much longer than a comparable SELECT with the same WHERE clause), the mostly likely causes are:

1. The rows that your are updating are locked by another session (doing a SELECT FOR UPDATE NOWAIT on these rows will make sure that you have the lock).
2. You have triggers that perform additional work,
3. You're updating a column referenced by a non-indexed foreign key.

Answer 2

Why you don't just

update table_name 
set start_date = systimestamp 
where column='Q'

If you suspect there are locks on the table, there are some tables to check: dba_locks, v$session, v$session_blockers etc. These are useful when a user blocked something with an accidental update without a commit or rollback, but you should be able to see if can exists blocking locks from the architecture of your application. You should just simulate on paper all the scenarios.