Optimization of nested SQL queries revisited
SIGMOD '87 Proceedings of the 1987 ACM SIGMOD international conference on Management of data
The structure of the relational database model
The structure of the relational database model
Optimization and dataflow algorithms for nested tree queries
VLDB '89 Proceedings of the 15th international conference on Very large data bases
Data models, database languages and database management systems
Data models, database languages and database management systems
Semantics for null extended nested relations
ACM Transactions on Database Systems (TODS)
Incremental computation of nested relational query expressions
ACM Transactions on Database Systems (TODS)
Cost-based optimization for magic: algebra and implementation
SIGMOD '96 Proceedings of the 1996 ACM SIGMOD international conference on Management of data
Outerjoin simplification and reordering for query optimization
ACM Transactions on Database Systems (TODS)
On optimizing an SQL-like nested query
ACM Transactions on Database Systems (TODS)
Orthogonal optimization of subqueries and aggregation
SIGMOD '01 Proceedings of the 2001 ACM SIGMOD international conference on Management of data
ICDE '96 Proceedings of the Twelfth International Conference on Data Engineering
Using EELs, a Practical Approach to Outerjoin and Antijoin Reordering
Proceedings of the 17th International Conference on Data Engineering
VLDB '87 Proceedings of the 13th International Conference on Very Large Data Bases
Aggregate-Query Processing in Data Warehousing Environments
VLDB '95 Proceedings of the 21th International Conference on Very Large Data Bases
Improved Unnesting Algorithms for Join Aggregate SQL Queries
VLDB '92 Proceedings of the 18th International Conference on Very Large Data Bases
Efficient processing of joins on set-valued attributes
Proceedings of the 2003 ACM SIGMOD international conference on Management of data
High-performance complex event processing using continuous sliding views
Proceedings of the 16th International Conference on Extending Database Technology
Efficient implementation of generalized quantification in relational query languages
Proceedings of the VLDB Endowment
| Hi-index | 0.00 |
One of the most powerful features of SQL is the use of nested queries. Most research work on the optimization of nested queries focuses on aggregate subqueries. However, the solutions proposed for non-aggregate subqueries are still limited, especially for queries having multiple subqueries and null values. In this paper, we show that existing approaches to queries containing non-aggregate subqueries proposed in the literature (including rewrites) are not adequate. We then propose a new efficient approach, the nested relational approach, based on the nested relational algebra. Our approach directly unnests non-aggregate subqueries using hash joins, and treats all subqueries in a uniform manner, being able to deal with nested queries of any type and any level. We report on experimental work that confirms that existing approaches have difficulties dealing with non-aggregate subqueries, and that our approach offers better performance. We also discuss some possibilities for algebraic optimization and the issue of integrating our approach in a relational database system.