Database system providing optimization of group by operator over a union all

A database system providing improved methods for processing a request for grouping of data from a plurality of database tables, said system comprising:

• a parser and normalizer module for receiving and parsing a request for grouping of data from a plurality of database tables;
• an optimizer module for converting said request into a logical tree;
• a transformation module for traversing said logical tree, examining each union node of said logical tree to determine if transformation of said union node is advantageous, and transforming each said union node of said logical tree for which transformation is determined to be advantageous by inserting grouping operators as children of said union node, said grouping operators enabling parallel processing of said plurality of separate database tables;
• and
• an execution module for execution of said logical tree against said plurality of separate database tables after transformation of said logical tree by said transformation module.

In a database system having a plurality of database tables, an improved method for query processing, the method comprising:

• receiving a query requesting grouping of data from a plurality of database tables;
• in response to said query, concurrently scanning data in each database table in said plurality of database tables;
• grouping data and generating summary results in parallel for each database table in said plurality of database tables;
• and
• merging said summary results from said plurality of database tables to produce a final aggregation result.