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'.
Concrete Patio Cost. A plain concrete slab usually costs $2 to $5 per square foot installed, depending on your region of the country. Decorative concrete patios start at about $6 to $10 per square foot for a simple design.Custom work involving borders, multiple colors and hand-application techniques costs $10 to $15 per square foot or more.oncrete Patio Cost. A plain concrete slab usually costs $2 to $5 per square foot installed, depending on your region of the country. Decorative concrete patios start at about $6 to $10 per square foot for a simple design.