Data integrity 
Integrity rules: the database system provides a wide range of declarative integrity rules, thus reducing the programming requirements for applications. Integrity rules that refer to a table can also be specified (see
constraint name).
Key: a key comprising one or more columns can be defined for each table. The database system ensures that each key is unique. A key can also consist of columns of different data types (see
key definition).
UNIQUE definition: the uniqueness of the values in other columns and column combinations can also be ensured by using other mechanisms (see
UNIQUE definition for "alternate keys").
NOT NULL: by specifying NOT NULL, you can ensure that the NULL value is not accepted in individual columns.
DEFAULT definition: you can define default values for each column (see
DEFAULT specification).
Referential integrity conditions: by specifying referential integrity conditions, you can declare deletion and existence dependencies between the rows in two tables (see
name of a referential constraint).
Database procedures and triggers: complex integrity rules that require access to further tables can be formulated with
database procedures or
triggers.