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This is documentation for Caché & Ensemble. See the InterSystems IRIS version of this content.

For information on migrating to InterSystems IRIS, see Why Migrate to InterSystems IRIS?

Unique

Specifies whether the index should enforce uniqueness.

Usage

To specify that Caché should enforce uniqueness for the properties on which this index is based, use the following syntax:

Index name On property_expression_list [ Unique ];

Otherwise, omit this keyword or place the word Not immediately before the keyword.

Details

The Unique keyword, if present, indicates that this is a unique index.

The property (or properties) indexed by a unique index are constrained to have unique values (that is, no two instances can have the same collated value) within the extent (set of all objects) of the class (table) that defines the index.

A unique index cannot also be a bitmap index.

Example

Index SSNIdx On SSN [ Unique ] ;

Default

If you omit this keyword, Caché does not enforce uniqueness for the properties on which this index is based.

See Also

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