SQL的查询速度优化方法

数据库查询是关系数据模型中关系操作的重要组成部分，而查询速度的快慢是系统是否优化的一个重要指标，也是当前网络数据库应用中所存在的瓶颈问题之一。本文从与数据库查询相关的索引、连接、Where子句等因素入手，结合实例分析了各因素对查询速度的影响，总结出根据表的不同情况选择聚簇索引或非聚簇索引对查询速度有明显影响：在组合索引中，使用频率高的字段应设置为前导列；建立充分的连接、优化Where子句对SQL的查询速度也有明显的提高。

Optimizing method for SQL query speed

Database query is one important part of relation-operation in relation-data model, and fast or slow of query speed is one important index that shows if the system is optimizing, at present, which is also one bottle-neck question of query speed in the network-database application. The paper starts with the related factors about database query ,such as index, link, where-clause, and analyses the affection about query speed of these factors with examples, and concludes that choosing cluster or non-cluster according to deferent tables will effect query speed distinctly. In combinatorial index, the high-frequency field should be set as leading column; setting up full linkage,and optimizing where-clause will improve SQL query speed obviously .