EVALUATION OF NUMBER OF PAGES TO BE ACCESSED DURING SCANNING OF RECORD DISK

摘要

PURPOSE: To accurately evaluate required page access during index scanning based on the level of the clustering of indexes and to select an access route by evaluating the number of data pages accessed during the index scanning of the table of a relational data base. CONSTITUTION: A data base table 10 provided with the rows 12 of employee data is physically stored on a data base 13 in the hiring order of employees. The table 10 is provided with a first index 14 for arranging the rows 12 in the increasing order of the alphabets of names, a second index 16 for arranging the rows in the ascending order of ages and a third index 18 for arranging the rows in the decreasing order of wages. The respective indexes 14, 16 and 18 are provided with many index entries 20 and the respective index entries 20 are provided with a key value 22 and a pointer or an identifier to one or more rows 12 provided with the key value.