Cache and Raid performance. One of the key limitations of spinning disk hardware is the use of a physical reading armature and the time this takes to move across the surface of a diskâs platter to the required data blocks.
Constraints are part of a database schema definition. A constraint is usually associated with a table and is created with a CREATE CONSTRAINT or CREATE ASSERTION SQL statement. They define certain properties that data in a database must comply with.
Syntax for the AUTO INCREMENT field is: column_name data_type constraint AUTOINCREMENT; column_name - is the name of the column (usually primary key) data_type - is the type of data column is storing. constraint  is the constraint definition (if any)