How to specify referential integrity between customer and Rep tables. Solution The purpose of using referential integrity is to prevent records that reference other records that do not exist. It also helps to keep references synchronized .Referential integrity is applied for a table relationship. Once enforced, Access rejects any operation that would violate referential integrity for that table relationship. Access rejects updates that change the target of a reference, and also deletions that remove the target of a reference. After referential integrity is applied, the following rules apply: A value cannot be entered in the foreign key field of a related table if that value doesn\'t exist in the primary key field of the primary table. If it happens, then records in the second table refer to records in the primary table which do not exist. They are called orphan records. Deleting a record from a primary table cannot happen if matching records exist in a related table, i.e deletion a record from the Customer table if there are orders assigned to that record in the rep table cannot take place. Primary key value cannot be changed in the primary table, if doing so would create orphan records. Example, you cannot change a customer number in the customers table if there are line items assigned to that customer in the rep table . The database enforces the rules of this relationship to maintain referential integrity by using a foreign key which allows declaring that an index in one table is related to an index in another and allows you to place constraints on what may be done to the table containing the foreign key. Syntax FOREIGN KEY [index_name] (index_columns) REFERENCES tbl_name (index_columns) Example SQL> create table customer(cust_id varchar2(10) primary key, cust_name varchar2(20)); SQL> create table rep(no number(3), cust_id varchar2(10) references customer(cust_id)); .

1. How to
specify referential integrity between customer and Rep tables.
Solution
The purpose of using referential integrity is to prevent records that reference other records that
do not exist. It also helps to keep references synchronized .Referential integrity is applied for a
table relationship. Once enforced, Access rejects any operation that would violate referential
integrity for that table relationship. Access rejects updates that change the target of a reference,
and also deletions that remove the target of a reference.
After referential integrity is applied, the following rules apply:
A value cannot be entered in the foreign key field of a related table if that value doesn't exist in
the primary key field of the primary table. If it happens, then records in the second table refer to
records in the primary table which do not exist. They are called orphan records.
Deleting a record from a primary table cannot happen if matching records exist in a related table,
i.e deletion a record from the Customer table if there are orders assigned to that record in the
rep table cannot take place.
Primary key value cannot be changed in the primary table, if doing so would create orphan
records. Example, you cannot change a customer number in the customers table if there are
line items assigned to that customer in the rep table .
The database enforces the rules of this relationship to maintain referential integrity by using a
foreign key which allows declaring that an index in one table is related to an index in another and
allows you to place constraints on what may be done to the table containing the foreign key.
Syntax
FOREIGN KEY [index_name] (index_columns) REFERENCES tbl_name
(index_columns)
Example

2. SQL> create table customer(cust_id varchar2(10) primary key, cust_name varchar2(20));
SQL> create table rep(no number(3), cust_id varchar2(10) references customer(cust_id));