嵌套查询的非嵌套化处理研究

嵌套查询是ＳＱＬ查询语言的重要特色，传统的数据为系统处理嵌套查询的方法是ＴＩＳ．ＴＩＳ方法处理效率很低。目前高嵌套查询处理效率的有效方法是非嵌套化处理方法。

UNNESTING ALGORITHMS FOR NESTED QUERIES

The SQL language allows users to express queries that have nested subqueries in them. Traditionally, database systems execute nested queries using Tuple iteration Semantics (TIS). However, TIS method is generally inefficient.Now, nested queries can be evaluated very efficiently by using unnesting method.This paper introduces new catalogs for nested queries, and describes unnesting translation rule for J type and linear JA type nested queries and optimization rule for JA unnesting results. Finally, integrated unnesting algorithms that can be easily implemented are given.