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Article #10317: Different types of dBASE Unique style indexes

Unique Indexes in dBASE tables have historically operated differently than unique indexes in other databases. Most or all other databases use unique indexes to prevent duplicate entries from being placed in a table. The way dBASE tables have worked is not to prevent duplicate entries from being entered in a table, but to only display unique values in the index when the index is selected.

One side effect of this technique is dealing with deleted records. If you delete the record which displays when the unique index is chosen, no values for the record deleted will be displayed even though they exist in the database until the database is packed.

When Visual dBASE 7 was released it offered a new way to create unique indexes. It added the new option of creating unique indexes which are distinct. Such indexes operate in the manner that most other database operate in that duplicate values are prohibited.

Visual dBASE can create and use either style of index. Delphi and C++ Builder can use either style index, but can only create distinct unique indexes. So, if you need to create unique indexes which are not distinct you must use Visual dBASE to create them.

Visual dBASE is owned by dBASE2000. For additional information on Visual dBASE see www.dbase200.com

Last Modified: 19-OCT-99