关键词: 代价估计, 元组, 查询, 属性

Abstract: In the operation of database, the proportion of the query operation is the largest, and query operation is the largest statement in cost. It is different that the cost is occurred by each type of operation during the data query operation. This paper combines with the applications of actual topic, proposes the estimation method of the operation cost of projection, option, joint, group and gathered and so on in the process of the query.

Key words: cost estimate, tuple, query, attribute