DOI: 10.5176/978-981-08-7656-2 A-41

Authors: Ms. G. Hemalatha, Dr. Thanuskodi K

Abstract: Query processing in relational database involves two parts: query execution and query optimization. Usually query execution takes more time than query optimization. The Most expensive part of query execution is Joins. Joins are statements that retrieve data from more than one table. A Join is characterized by multiple tables in the FROM clause, and the relationship between the tables is defined through the existence of a Join condition in the WHERE clause. In the case of Very large databases and highly normalized databases frequency of Join queries are high. To perform the Join Query much efficiently, the Join Method the optimizer selects are very vital. Nested Loop Join,
Hash Join and Merge Sort Join are primary Join methods available to join tables. The aim of this paper is to introduce the traditional join techniques and to compare the cost of these techniques. This paper also covers some of the recent
advancements in the Join Techniques. Join operations can be improved in two ways one in controlling the way in which tuples are stored ie., the physical storage of data such as partitioning the table, composite index, Join index, clustering of data tuples etc.,. Another way is to improve the technique used to Join the relation. A small change to the technique improves the performance of Join dramatically. This paper surveys the existing blocking Join
techniques.

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