Google and the Library Databases, in large part, search for different types of material. Google searches the World Wide Web for information most of which can be freely viewed by anyone with a connection to the Internet. Library databases search for published material that the library pays for you to be able to access.
Published material found through the library databases has already gone through several reviewers to determine its authority and reliability before it ends up on your computer screen. Many sources on the web found using Google have not been reviewed at all, so the responsibility for determining authority and reliability falls to you.
Try using this Website Evaluation Checklist when deciding if you want to use information found online.
You can also complete this tutorial on Choosing the Best Web Source to learn more.