Primary Table Key
Each internal table has a primary table key that is either a self-defined key or the standard key. For hashed tables, the primary key is a hash key, for sorted tables, the primary key is a sorted key. Both of these table types are key tables for which key access is optimized and the primary key thus has its own administration. The key fields of these tables are write-protected when you access individual rows. Standard tables also have a primary key, but the corresponding access is not optimized, there is no separate key administration, and the key fields are not write-protected.