1. A computer implemented method comprising: merging a plurality of base synopses to generate a merged synopsis, wherein each base synopsis summarizes a statistic for a portion of a table, and wherein each base synopsis contains values for a respective defined region of a domain of values, wherein the merging includes performing the following: for each value that is any of the plurality of base synopses and is in a intersection of the respective defined regions, if the value does not exist in the merged synopsis, adding the value to the merged synopsis; after merging the plurality of base synopses to generate the merged synopsis, estimating the statistic based on a number of values in the merged synopsis and a size of the intersection of the respective defined regions relative to a size of the domain; and wherein the method is performed by one or more computing devices.