Skinny tables can contain a maximum of 100 columns.
Skinny tables cannot contain fields from other objects.
Skinny tables are not copied to sandbox organizations. To have production skinny tables activated in a sandbox organization, contact salesforce.com Customer Support.
Considerations
Skinny tables can contain a maximum of 100 columns.
Skinny tables can’t contain fields from other objects.
For Full sandboxes: Skinny tables are copied to your Full sandbox orgs.For other types of sandboxes: Skinny tables aren’t copied to your sandbox organizations. To have production skinny tables activated for sandbox types other than Full sandboxes, contact Salesforce Customer Support.