| 摘要: |
| 直方图是许多商用数据库系统中最常用的一种估算查询结果大小的方法.从实用的观点来看，过去已提出的一些直方图方法有局限性，主要是它们不能保证估算值的准确程度.本文将提出两种新的直方图方法，它们不仅使用方便，而且可以保证所有的估算值均在给定的误差范围内.此外，本文还探讨了不同的数据分布对直方图的影响，通过运用一些重要的参数刻画数据分布，用以帮助生成效果较佳的直方图. |
| 关键词: 数据库系统，查询优化，查询代价的估算，直方图. |
| DOI： |
| 分类号: |
| 基金项目:本文研究得到国家自然科学基金资助. |
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| Histogram Method for Size Estimation of Query Result |
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WU Sheng-li
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| Abstract: |
| Histogram is the commonest method for the size estimation of query result in many commercial database systems. Several histogram methods presented in the past have certain limitations in practicability due to their lack of guarantee of the accuracy of the estimation. In this paper, the author presents two kinds of new histogram methods, which are easy to use and can guarantee the accuracy of the estimation. Otherwise, the effect of different data distributions to histograms is discussed in the paper, and some important parameters of data distribution are introduced to help produce better histograms. |
| Key words: Database systems, query optimization, estimation of query cost, histogram. |
