MDAC 2.5 SDK - ODBC Desktop Database Drivers
When the Microsoft Access, dBASE, or Paradox driver is used, the ALTER TABLE statement is supported with add and drop table constraint definition clauses. (ALTER TABLE statements are not supported for the Microsoft Excel or Text drivers.)
Note When you use the Paradox driver without implementing the Borland Database Engine, ALTER TABLE statements are not supported; only read and append statements are allowed.