A computer system affords a user the ability to interactively formulate, visualize, and modify query plans that are to be posed to a database. The computer system provides query visualization in the form of decision trees having nodes selectable/deselectable to search for alternative query plans with lower or minimum execution time. The estimated cost and/or the execution time of a subtree of a query plan may be mapped according to a rectangle area metaphore, with the area of a rectangle enclosed by a larger rectangle representing a parent node in the plan tree. Query plans may be saved by the system in order to facilitate their visualization, optimization, and/or modification at a later date.