Need to contact Salesforce Customer Support or your Account Manager to enable skinny tables.
It can be created on custom objects, and on Account, Contact, Opportunity, Lead, and Case objects.
Here is an example from Salesforce Documentation:
This table shows an Account view, a corresponding database table, and a skinny table that would speed up Account queries.
Skinny tables can contain the following types of fields.
- Date and time
- Phone picklist
- Picklist (multi-select)
- Text area
- Text area (long)
Few points to remember:
- Can contain a maximum of 100 columns.
- Cannot contain fields from other objects.
- Data only copied to Full Sandboxes, but can be activated for other sandboxes on request.