the easiest way i can think of is to use a plugin that creates a form by shortcode like contact form 7 for example and I’ll break it in to easy steps.
-
Create the form on your main site or
what ever site you would like to
manage the forms data through. -
Create a page template with no header or footer just a plain loop and call
the_content
. -
Create a new page , add the Form’s
shortcode to it and set the template
as your new page template. -
Get the URL of that page and create
an iframe to it. -
On each site you would like to show
the form just add the Iframe code to
a sidebar text widget.
and that should do it.
Oh wait, you will probably need to add Contact form 7’s Javascripts and css and i just read your question again and you are looking to save this forms in to database and since this plugin does’nt save to database on its own you can use an extenstion plugin called Contact Form 7 to Database or use a different forms plugin all together.
Hope this helps