How do you create a composite unique key?

How do you create a composite unique key?

A composite unique key is a unique key made up of a combination of columns. Oracle creates an index on the columns of a unique key, so a composite unique key can contain a maximum of 16 columns. To define a composite unique key, you must use table_constraint syntax rather than column_constraint syntax.

How do I create a unique constraint in Oracle?

The syntax for creating a unique constraint using an ALTER TABLE statement in Oracle is: ALTER TABLE table_name ADD CONSTRAINT constraint_name UNIQUE (column1, column2, column_n);

How do I remove unique restrictions?

To delete a unique constraint using Table Designer

1. In Object Explorer, right-click the table with the unique constraint, and click Design.
2. On the Table Designer menu, click Indexes/Keys.
3. In the Indexes/Keys dialog box, select the unique key in the Selected Primary/Unique Key and Index list.
4. Click Delete.

Which is an example of restriction in XML?

The value must be minimum five characters and maximum eight characters: This example shows a complex type definition using restriction. The complex type “Norwegian_customer” is derived from a general customer complex type and its country element is fixed to “Norway”:

Can a complex type be used in an instance?

An indicator of whether the complex type can be used in an instance document. If this value is true, an element cannot use this complex type directly but must use a complex type derived from this complex type.

How to create and disable unique constraints in Oracle?

This Oracle tutorial explains how to create, drop, disable, and enable unique constraints in Oracle with syntax and examples. A unique constraint is a single field or combination of fields that uniquely defines a record. Some of the fields can contain null values as long as the combination of values is unique.

Which is an example of a schema restriction element?

The value of age can NOT be lower than 0 or greater than 100: This example also defines an element called “initials”. The “initials” element is a simple type with a restriction. The only acceptable value is THREE of the LOWERCASE OR UPPERCASE letters from a to z: This example defines an element called “password”.