1. A method for querying a distributed database system, the method comprising: parsing, by one or more processors, a query request; generating, by one or more processors, an access plan for the query request, wherein the access plan specifies therein a database table related to the query request, and wherein a copy of the database table is stored in multiple database devices; selecting, by one or more processors and based on status information of each copy of the database table, one copy of the database table from a plurality of copies of the database table as a target database table; and executing, by one or more processors, a query operation on the target database table according to the access plan.