Query optimization through the use of multi-column statistics to avoid the problems of non-indexed column correlation

摘要: The system, method, and program of this invention collects multi-column statistics, by a database management system, to re? ect a relationship among multiple columns of a table in a relational database. These statistics are stored in the system catalog, and are used during query optimization to obtain an estimate of the number of qualifying roWs When a query has predicates on multiple columns of a table.A multi-column linear quantile statistic is collected by dividing the data of multiple columns into sub-ranges Where each sub-range has approximately an even distribution of data, and determining a frequency and cardinality of each sub-range. A multi-column polygonal quantile statistic is collected by dividing the data of multiple columns into sub-spaces Where each sub-space contains approximately the same number of tuples, and determining a frequency and cardinality of each sub-space.