Customer-->ID primary key
CustomerTicket-->ID,TicketNo where ID,TicketNo are foreign-key
Ticket-->TicketNo,Subject where TicketNo primary key

ID TicketNo Subject
1  12        Car
1  18       Home
2  23       Plane

Gridview.DataSource=from customer in entity.Customer
join custicket in entity.CustomerTicket on customer.ID equals custicket.ID .....