A database system comprises an interface for a storage device, and a control device for accessing the storage device through the interface. The storage device stores a table that manages a plurality of rows comprising a plurality of item values, and an index configured in a tree structure based on a plurality of nodes enabling to identify the rows by using one or more item values. The control device identifies an item value condition included in a search condition of a search query, determines whether or not the node of the index corresponding to the item value condition is reference-disabled, and when the node is reference-disabled, identifies a range of item values managed by the reference-disabled node, and searches for a row that satisfies the search condition for the identified range.