Difference between Index column and simple column in SharePoint?

Question

Difference between Index column and simple column in SharePoint?

What is the need of creating index column ?

Answer 1

An indexed column in SharePoint makes sense to improve performances.
If your list contain a lot (~1000s) of records, and you often query (filter or sort) by a given column, you can index that column. That way, when displaying a filtered/sorted view (based on this column), SharePoint does not have to loop throuh all the items to decide whitch ones to display (firts): thanks to the index it can quickly get the elements it needs.

A lot of articles on the Web can be found, that discuss the topic deeply:

• Official doc: https://support.office.com/en-us/article/Manage-lists-and-libraries-with-many-items-b8588dae-9387-48c2-9248-c24122f07c59#__creating_sharepoint_indexed
• How it works Under the Hood: http://apmblog.dynatrace.com/2009/01/28/sharepoint-list-performance-how-list-column-indices-really-work-under-the-hood/
• Some tips: http://www.learningsharepoint.com/2013/12/16/things-to-note-about-indexed-columns-in-sharepoint/
• Another one on SE: Should i index all columns in a list?

As you can see, it's only a matter of googling something like "sharepoint indexed column"...