An item for designating a time stamp accuracy is added to an inquiry syntax of a query. At the time of table coupling, a query designating the desired accuracy in the item is transmitted. This query is analyzed by a query parser, and individual queries are created for each database targeted for inquiry and transmitted. At the time of coupling acquired tables, the number of digits of the time stamps is adjusted to be the same in accordance with the designated accuracy, and the tables are coupled in chronological order of the time stamps.