Can I get databse connected with forms inorder to validate it??

Yes it is very much possible to Post or Export the form submission data to a database like MySQL database.

You can check the App here http://apps.jotform.com/app/mysql_export

OR you can also do it using a bit of PHP and Post data method. Follow this user guide

http://www.jotform.com/help/126-How-to-send-Submissions-to-Your-MySQL-Database-Using-PHP

Please let us know if you have any other question.

let me explain you what I actually need... Whenever the user enters the id the remaining fields should automatically get filled with corresponding data if the id is already present in the excel sheet.

I would recommend you use the Spreadsheet to Form widget: Please find the widget here: https://widgets.jotform.com/widget/spreadsheet_to_form 

Here is also a guide that will help you to implement the widget on your form: https://www.jotform.com/help/442-How-to-Use-the-Spreadsheet-to-Form-Widget 

I hope this helps.