Processing UNION and UNION ALL Operators in Relational Data Base Accessing Systems
Original Publication Date: 1987-Jul-01
Included in the Prior Art Database: 2005-Feb-01
This invention relates to a method for processing the table results from a sequence of relational data base queries with selectively embedded UNION and UNION ALL operators. The method includes the steps of clustering and executing predetermined UNION and UNION ALL operators upon the results in order to eliminate redundant rows. The processing sequences are not commutative. UNION is a well-known set operator which combines two sets into one and every element in the result set is distinct. In relational data base systems, a query generates a table as its result. The results of two queries can be combined together by a UNION operator which removes the duplicated rows and keeps every row in the result table distinct.