An index structure for use by a database management system comprises a variant of a Patricia tree, wherein each node stores a column value that identifies a specified column of the constructed n-column search key that is used to determine a next path taken through the tree, a null value N that specifies whether a null value or an actual data value of the specified column of the constructed n-column search key is used to determine the next path taken through the tree, and a position value that specifies a portion of the specified column from the constructed n-column search key to be used to determine the next path taken through the tree when the actual data value of the specified column of the constructed n-column search key is used to determine the next path taken through the tree.