Hi all whenever I type w3schools in Google, this is what is displayed:
I believe that these things are called Google Sitelinks.
I was wondering why is it that some sitelinks have a search bar while others don't have one?
Just like with the Sitelinks Google decides if it will add it or not. The criteria is not public and you do not have any control over whether it will appear or not. Although having built in search functionality in your site probably helps out a whole lot I am sure.