Oracle / PLSQL: Enable a foreign key

This Oracle tutorial explains how to enable a foreign key in Oracle with syntax and examples.

Description

You may encounter a foreign key in Oracle that has been disabled. You can enable the foreign key using the ALTER TABLE statement.

Syntax

The syntax for enabling a foreign key in Oracle/PLSQL is:

ALTER TABLE table_name
ENABLE CONSTRAINT constraint_name;

Example

If you had created a foreign key as follows:

CREATE TABLE supplier
( supplier_id numeric(10) not null,
  supplier_name varchar2(50) not null,
  contact_name varchar2(50),
  CONSTRAINT supplier_pk PRIMARY KEY (supplier_id)
);

CREATE TABLE products
( product_id numeric(10) not null,
  supplier_id numeric(10) not null,
  CONSTRAINT fk_supplier
    FOREIGN KEY (supplier_id)
    REFERENCES supplier(supplier_id)
);

In this example, we've created a primary key on the supplier table called supplier_pk. It consists of only one field - the supplier_id field. Then we've created a foreign key called fk_supplier on the products table that references the supplier table based on the supplier_id field.

If the foreign key had been disabled and we wanted to enable it, we could execute the following command:

ALTER TABLE products
ENABLE CONSTRAINT fk_supplier;