How can I set a custom date time format in Oracle SQL Developer?

You can change this in preferences:

1. From Oracle SQL Developer's menu go to: Tools > Preferences.
2. From the Preferences dialog, select Database > NLS from the left panel.
3. From the list of NLS parameters, enter DD-MON-RR HH24:MI:SS into the Date Format field.
4. Save and close the dialog, done!

Here is a screenshot:

I stumbled on this post while trying to change the display format for dates in sql-developer. Just wanted to add to this what I found out:

• To Change the default display format, I would use the steps provided by ousoo i.e Tools > Preferences > ...

• But a lot of times, I just want to retain the DEFAULT_FORMAT while modifying the format only during a bunch of related queries. That's when I would change the format of the session with the following:

  alter SESSION set NLS_DATE_FORMAT = 'my_required_date_format'

Eg:

   alter SESSION set NLS_DATE_FORMAT = 'DD-MM-YYYY HH24:MI:SS' 

With Oracle SQL Developer 3.2.20.09, i managed to set the custom format for the type DATE this way :

In : Tools > Preferences > Database > NLS

Or : Outils > Préférences > Base de donées > NLS

YYYY-MM-DD HH24:MI:SS

Note that the following format does not worked for me :

DD-MON-RR HH24:MI:SS

As a result, it keeps the default format, without any error.