摘要
在数据库操作中查询操作所占比重最大,而查询操作所基于的SELECT语句在SQL语言中又是代价最大的语句。结合实际课题应用,提出了基于关系代数树结构的SQL查询优化策略。利用改进查询计划的代数定律,分析基于关系代数树的关系代数式查询优化方法、研究关系代数表达式与SQL查询的等价变换准则、分析关系代数表达式等价变换前后的查询代价;通过实验、实例以及代价估计验证了利用关系代数树改进数据库查询优化操作的优势。
In the operation of database,the proportion of the Query operation is the largest.And SELECT statement in the SQL language as the base of query operation is the largest statement in cost.In accordance with the actual topic applications,SQL query optimization strategy based on the relational algebra tree structure is put forward.By making use of the algebra law,this paper tries to work out an optimal query method based on relational algebra tree,to analyze the equivalent transformation rules between the relational algebra expressions and the SQL query,and to make clear of the query cost before and after the equivalent transformation of the relational algebra expressions.Through the experiments & examples & cost estimate,the advantage that using the relational algebra tree improve the operation of query optimization to the database was verified.
出处
《电子设计工程》
2012年第7期5-8,12,共5页
Electronic Design Engineering
基金
四川省教育厅高等学校重点科研项目(11ZA178)
关键词
关系代数树
查询优化
选择
投影
连接
代价
relational algebra tree
query optimization
option
projection
joint
cost
