1. A database system comprising: a storage unit that stores a database including an entity data group containing a plurality of entity data, a plurality of identifier tables each having only fixed-length data and each having, as the fixed-length data, a reference identifier and a data identifier in each tuple of a plurality of tuples that eliminates overlap with other identifier tables, and a reference table having the reference identifiers in each tuple, wherein the data identifier uniquely indicates one of the plurality of entity data, and the reference identifiers in each tuple of the reference table uniquely indicate the data identifiers in the different identifier tables, wherein each reference identifier of the set of reference identifiers in the tuple of the reference table uniquely identifies one of the data identifiers stored in one of the identifier tables; and a transaction processing unit that receives a query and performs transaction processing on the database on the basis of the received query using the reference table and the identifier tables and transmits a result of the transaction processing back to a device that initiated the query, wherein the transaction processing unit: converts a data record into a reference record including reference identifiers; adds the reference record as one tuple to the reference table; determines whether all of the reference identifiers included in the added tuple have already been stored in one or more of the other tuples in the reference table; when it is determined that the reference identifiers have not already been stored, adds a new data identifier corresponding to one of the reference identifiers included in the added tuple to one of the plurality of identifier tables and adds new entity data corresponding to the new data identifier to the entity data group; and when it is determined that the reference identifiers have already been stored, ends further processing of the data record after adding the reference record to the reference table without adding the new data identifier and the new entity data.