问题: Consider a relation of scheme Building(Street, Number, No.Apartments, Color, Age).
TRC: find the oldest building in Downing Street.
相关的SQL语句应该是: SELECT MAX(Age) AS ‘Oldest building’, Street FRO
关系代数与关系演算的确切区别是什么?在大多数的参考,它将是 Relational algebra is procedural and calculus is non procedural。 那么,这些代表什么。但是,我们可以使用关系 代数来解决所有问题。那么为什么我们会使用关系演算。除定义外,非常感谢与例子的解释。
我试图将sql查询转换为元组关系演算,但有一个NOT EXIST导致我被卡住。 SQL查询: SELECT num FROM a a1, b b1
WHERE a1.num = b1.no AND a1.name = "Tim"
AND NOT EXIST
(SELECT * FROM a a2, b b2
WHERE a2.num = b2.no AND a2.name