Indexes

NOTE: If you define an index using the Btrieve driver, the index will not have the restrictions discussed here.

For query optimization, the Btrieve driver does not use the following:

Indexes containing all-segment-null keys or any-segment-null keys.
Any index key that is marked case-insensitive.
Any index keys where the data type of the index key does not match the data type of the field. The one exception is if the index key is declared as an unsigned integer and the field in the file is declared as signed integer, or vice versa, then the driver assumes the field contains only unsigned quantities and uses the index. Note that this can lead to incorrect results if the field in fact does contain signed quantities.

The Btrieve driver only uses an alternate-collating-sequence (ASC) index key for equality lookups. Additionally, if an ASC key is part of a segmented index, the other index segments are not used for query optimization unless the Where clause contains an equality condition for the ASC key.