[Fixed]-Adding fields to an already existing database for Django (version < 1.7)

This answer is still getting visibility but is outdated. Since 1.7 Django ships with a built-in migration system, written by the same author as South, and has deprecated syncdb though it will still work.

You will simply need to run a few commands to automatically add new columns:

python manage.py makemigrations  
python manage.py migrate

It will be useful to understand what’s happening under the hood, but those are the basics. Please ask new questions to get answers on 1.7 and migrations if you are still reading this old post.

For django < 1.7

syncdb will not add any new columns. See
http://docs.djangoproject.com/en/dev/ref/django-admin/#syncdb

You will have to add them manually. For example,. replace <> with relevant info:

python manage.py dbshell
ALTER TABLE <appname_modelname> ADD COLUMN <column_type> DEFAULT '';

You can see what Django might have done to generate columns on a fresh syncdb by using:

python manage.py sqlall app_name

and copying and pasting ALTER TABLE statements from there.

Otherwise, you can look into third-party apps like Django-South which are database migration tools.

There are other options of migration apps (although South is the most used).

I have used django-evolution for my projects and it was very easy to install and start using.

South seems to be more complete, but for simpler tasks, django-evolution may be suitable.