Multi-objective optimization is the problem of optimizing simultaneously multiple objective functions and several techniques exist to deal with this problem. This paper aims to present the main methods that can be used to solve this issue in the context of relational databases. In particular, this work examines Top-k query to get the k best result from a dataset and Skyline query that provides a more general overview of the best results. We also discuss Flexible-skyline, a new method designed to improve upon the previous techniques, mitigating their shortcomings. For each method, we describe the main characteristics and present an overview of the algorithms implementing such thecniques, while comparing advantages and disadvantages.

翻译：多目标优化是同时优化多重客观功能的问题,为解决这一问题,存在几种技术。本文件旨在介绍在关系数据库范围内解决这一问题的主要方法,特别是,这项工作审查Top-k查询,以便从数据集和天空线查询中取得k最佳结果,更全面地概述最佳结果。我们还讨论灵活天空线,这是一种新方法,旨在改进以前的技术,减少其缺点。我们为每一种方法描述主要特点,并概述执行这种分类法的算法,同时比较利弊。