设有一个SPJ数据库，包括S，P，J，SPJ四个关系模式,用关系代数完成查询和用SQL完成各项操作-SPJ has a database, including S, P, J, SPJ four model, using relational algebra and the use of SQL query to complete the operation completed

transformation of sql query into relational algebra

关系代数，关系演算和关系模型的学习课件，用于对数据库系统的入门指导。-Relational algebra, relational calculus and the relational model of learning courseware for introductory guide for database systems.