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 countertop cost: $75-$125 per square foot for most installations, though costs can be slightly higher for complex concrete designs Maintenance costs: Moderate to high How to save money on concrete countertops: Keep the design simple using rectangular sections and straight lines with a square or slightly rounded edge.