1. A computer implemented method for providing an approximate answer to a query in a stored relational database, the method comprising the steps of: receiving said query containing input data to said stored relational database; precomputing a summary of a data cube corresponding to said stored relational database by defining at least one sub-cube; summarizing said at least one sub-cube using a plurality of histogram techniques; computing an error/space benefit for each summary of said at least one sub-cube corresponding to each histogram technique; determining a maximum of the error/space benefits, wherein said maximum error/space benefit corresponds to a summary with a minimum error; calculating an approximate answer to said query based on said input data using the histogram technique corresponding to said maximum error/space benefit; and outputting said approximate answer.