Unique Property

See Also   Applies To

Sets or returns a value that indicates whether an CdbIndex object represents a unique (key) index for a table (Microsoft Jet workspaces only).

Syntax

VOIDSetUnique(BOOL bFlag );

BOOLGetUnique(VOID);

Parameters

Remarks

For a CdbIndex object, this property setting is read/write until the object is appended to a collection, after which it's read-only.

A unique index consists of one or more fields that logically arrange all records in a table in a unique, predefined order. If the index consists of one field, values in that field must be unique for the entire table. If the index consists of more than one field, each field can contain duplicate values, but each combination of values from all the indexed fields must be unique.

If both the Unique and Primary properties of a CdbIndex object are set to True, the index is unique and primary: It uniquely identifies all records in the table in a predefined, logical order. If the Primary property is set to False, the index is a secondary index. Secondary indexes (both key and nonkey) logically arrange records in a predefined order without serving as an identifier for records in the table.

Notes

• You don't have to create indexes for tables, but in large, unindexed tables, accessing a specific record can take a long time.
  
  
• Records retrieved from tables without indexes are returned in no particular sequence.
  
  
• The Attributes property of each CdbField object in the CdbIndex object determines the order of records and consequently determines the access techniques to use for that CdbIndex object.
  
  
• A unique index helps optimize finding records.
  
  
• Indexes don't affect the physical order of a base table — indexes affect only how the records are accessed by the table-type CdbRecordset object when a particular index is chosen or when the Microsoft Jet database engine creates Recordset objects.