摘要
嵌套查询是ＳＱＬ查询语言的重要特色．传统的数据库系统处理嵌李查询的方法是ＴＩＳ．ＴＩＳ方法处理效率很低．目前提高嵌套查询处理效率的有效方法是非嵌套化处理方法．本文通过刻画相关嵌套查询的基本特性，给出了相关嵌套查询的进一步分类，并讨论了Ｊ类和线性ＪＡ类嵌套查询非嵌套化的转换规则和非嵌套化后的优化处理策略，最后给出易于实现的非嵌套化处理算法．
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.
出处
《计算机学报》
EI
CSCD
北大核心
1995年第4期241-251,共11页
Chinese Journal of Computers
