Types of primary keys All database tables must have one primary key column. The primary key uniquely identifies a row within a table therefore it’s bound by the following constraints: UNIQUE NOT NULL IMMUTABLE When choosing a primary key we must take into consideration the following aspects: the primary key may be used for joining other tables through a foreign key relationship the primary key usually has an associated default index, so the more compact the data type the less space the index will take the primary key assignment must ensure uniqueness… Read More