Which statement is correct about informational constraints?
A.
An informational constraint can be used by the SQL compiler to improve the access to data and
query performance.
B.
The database manager uses an informational constraint to enforce the uniqueness of the key
during changes to the columns of the unique constraint.
C.
An informational constraint is a column or combination of columns that
has the same properties as a unique constraint.
D.
An informational constraint specifies that every row that is inserted or
updated in the table must conform to the definition of the table.