A.They define a relationship between two tables.

B.They ensure that a column only contains NULL values.

C.They enforce the uniqueness of values in a column.

A.Employees who have managers

B.Employees and their managers' IDs

C.All employees and their IDs

D.Employees who do not have managers

A.To automatically generate numeric values for a column

B.To improve query performance

C.To provide simplified and consistent access to an object

D.To enforce unique constraints on a table

A.=

B.NOT NULL

C.EXISTS

D.IN

A.To create new tables and indexes

B.To increase query performance

C.To control user access to database objects and operations

D.To define the structure of database tables