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_nameENABLE 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 productsENABLE CONSTRAINT fk_supplier;