Entity Primary Text Field from database

CRM is storing all attributes in Attribute table and all entities into Entity table.

In database CRM is using ColumnNumber and IsCustomField columns to identify attribute is custom or not.

IsCustomField=1 means custom filed.

If you want to find Entity primary text field then use following query

select EntityView.Name, EntityView.PhysicalName, AttributeView.Name, AttributeView.PhysicalName from AttributeView

inner join EntityView

on

EntityView.EntityId=AttributeView.EntityId

where ColumnNumber<33 and IsCustomField=1

ColumnNumber < 33 are all system attributes for that entity and ColumnNumber > 33 are all custom attributes for that entity in Attribute Table.  

Open Entity Form from Entity Ribbon custom button

To open any entity form from custom button added in entity grid ribbon just add following code in action section.

       when pass Entity Object Type code as a value to IntParameter, then CRM will open that entity form. 
e.g. If wants to open account form from custom button shown on Activity grid ribbon, then use
IntParameter Value="1"