1. An apparatus for processing a query for a NoSQL database, the apparatus comprising: a storage unit configured to store (i) a plurality of safe elements committed and saved in the database, and (ii) a plurality of unsafe elements for updating the plurality of safe elements, wherein the unsafe elements are not committed or committed, but not saved as committed data; a first query executing unit configured to execute the query on the plurality of unsafe elements, wherein the first query executing unit determines whether or not to include a specific unsafe element extracted using the query among the plurality of unsafe elements in a result of the query based on a state of transaction relating to updating with the specific unsafe element; a second query executing unit configured to execute the query on the plurality of safe elements after the first query executing unit executes the query, wherein the second query executing unit determines whether or not to include a specific safe element extracted using the query among the plurality of safe elements in a result of the query based on a state of transaction relating to updating the specific safe element; and a third query executing unit configured to execute the query on at least one safe element saved during execution of the query by the second query executing unit after the second query executing unit executes the query, wherein the third query executing unit determines whether or not to include a specific safe element extracted using the query among the at least one safe element in a result of the query based on a state of transaction relating to updating the specific safe element.