|
A nested loop join is a naive algorithm that joins two sets by using two nested loops. Join operations are important to database management. ==Algorithm== Two relations and are joined as follows: For each tuple r in R do For each tuple s in S do If r and s satisfy the join condition Then output the tuple This algorithm will involve nr *bs+ br block transfers and nr+br seeks, where br and bs are number of blocks in relations R and S respectively, and nr is the number of tuples in relation R. The algorithm runs in I/Os, where and is the number of tuples contained in and respectively. Can easily be generalized to join any number of relations. The block nested loop join algorithm is a generalization of the simple nested loops algorithm that takes advantage of additional memory to reduce the number of times that the relation is scanned. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「nested loop join」の詳細全文を読む スポンサード リンク
|