Database retrieving method, apparatus and storage medium thereof

摘要

A comparison between a cost required when retrieval is performed after an index corresponding to a retrieval condition is generated and a cost required when entire retrieval is performed is made. If the cost required when the entire retrieval is performed is higher, it is determined whether or not an applicable index exists among already generated indexes. If an applicable index does not exist, an index corresponding to the retrieval condition is generated. A database is then retrieved by using the generated index.