Which of the following ensures referential integrity between tables?

A.
Foreign key

B.
CHECK constraint

C.
Index

D.
Primary key

Explanation:
The foreign key ensures referential integrity between tables. A foreign key is a column or
combination of columns used to establish and enforce a relationship between the data in two tables.
This relationship is created by adding a column(s) in one of the tables to refer to the other table’s
column(s) protected by a PRIMARY KEY or UNIQUE constraint. This column becomes a foreign key in
the first table. A foreign key can be created by defining a FOREIGN KEY constraint when creating or
altering a table.