A primary key is a candidate key that is most appropriate to be the main reference key for the table. As its name suggests, it is the primary key of reference for the table and is used throughout the database to help establish relationships with other tables.
1 A concrete driveway with several decorative elements can cost $12 -$18 a square foot, or $3,600 -$5,400 for 12'x25' or $11,500 -$17,500 for 24'x40'.
The overall cost of a concrete patio depends on the design and size of the patio. Prices usually start at around $6 per square foot up to $10 per square foot for a basic design without any colors or special designs. Adding colors or a pattern to the design can increase the price to $15 per square foot.