1. A method implemented on a general-purpose computing device for discovering and expressing query hints in a database management system, comprising: using the general-purpose computing device to perform the following: input a query having an initial query execution plan; computing a direct acyclic graph for the query; constraining the query using a power hints query language expression; computing candidate matches for each operator in the initial execution plan; extracting a revised query execution plan having a lowest cost as determined by a query optimizer cost model that satisfies constraints of the power hints query language expression; displaying the revised query execution plan in a graphical manner to a user; and allowing the user to change the revised query execution plan if the user is not satisfied with the revised query execution plan.