1. A 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 the intersection of the respective defined regions, if the value does not exist in the merged synopsis, adding the value to the merged synopsis; and after merging the plurality of base synopses to generate the merged synopsis, estimating the statistic based on the number of values in the merged synopsis and the size of the intersection of the respective defined regions relative to the size of the domain.