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dBASE Indexes

  • Artikkeli

The ODBC dBASE driver automatically opens and updates dBASE IV index files. You must use the Select Indexes dialog box displayed through the ODBC Data Source Administrator to associate dBASE III .ndx files with dBASE files.

The following limitations apply to the creation of dBASE indexes:

  • All column names must be valid.

  • All columns must be in the same ascending or descending order.

  • The length of any single text column must be less than 100 bytes.

  • If more than one column exists, all of the columns must be text columns and the sum of the column sizes must be less than 100 bytes.

  • Memo fields cannot be indexed.

  • An index must not be specified for the current set of fields (that is, duplicate indexes are not allowed).

  • The index name must match the dBASE index naming convention. dBASE III requires that each index be in a separate file, each having an .ndx extension. In dBASE IV, indexes are created as tag names that are stored in a single .mdx file. The .mdx file has the same base name as the database file (for example, Emp.mdx is the index file for the Emp.dbf database).

  • dBASE defines a unique index as one where only one record from a set with identical key values is added to the index.