Selection Operation File scan-search algorithms that locate and retrieve records that fulfill a selection condition. Algorithm A1 (linear search).Scan each file block and test all records to see whether they satisfy the selection condition. Cost estimate b,block transfers +1 seek b,denotes number of blocks containing records from relation r If selection is on a key attribute,can stop on finding record cost =(b,/2)block transfers +1 seek Linear search can be applied regardless of selection condition or ordering of records in the file,or availability of indices Database System Concepts-5th Edition,Aug 27,2005. 13.9 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 5 13.9 ©Silberschatz, Korth and Sudarshan th Edition, Aug 27, 2005. Selection Operation File scan – search algorithms that locate and retrieve records that fulfill a selection condition. Algorithm A1 (linear search). Scan each file block and test all records to see whether they satisfy the selection condition. Cost estimate = br block transfers + 1 seek  br denotes number of blocks containing records from relation r If selection is on a key attribute, can stop on finding record  cost = (br /2) block transfers + 1 seek Linear search can be applied regardless of  selection condition or  ordering of records in the file, or  availability of indices