1解析与翻译( Parsing and translation) 2.优化( Optimization) 3.评估( Evaluation) parser and relational-algebra query translator expression optimizer 4 execution plan output evaluation engine data about data 查询处理过程查询处理过程 1. 解析与翻译(Parsing and translation) 2. 优化(Optimization) 3. 评估(Evaluation)