What kind of connection is used to attach the legs to this table?
It could possibly be done using Mortise and Tenon joints, however, it looks like this table simply uses  Hanger Bolts. 

 

If you look at a picture from the bottom of the table,



you'll notice there are holes bored in the underside of the table top.  This is likely where the nut would be attached to the bolt, which is in turn screwed into the leg.