关系代数中的算术除法
Arithmetic division in relational algebra
我有一个 SQL 请求：
SELECT table1.nr1 / NULLIF(table2.nr2, 0) as percentage
我想用关系代数来写这个。
可以用关系代数表示算术除法吗？
根据this course of the University of Rochester关系代数可以定义为
a formal system for manipulating relations
- Operands of this algebra are relations.
Operations of this algebra include the usual set operations (since relations are sets of tuples), and special operations defined for relations
selection
projection
join
这是一门关于关系的代数，没有数字的表示。如果你想对数字使用算术，你必须使用扩展的形式主义，例如 Safe Database Queries with Arithmetic Relations.
我有一个 SQL 请求：
SELECT table1.nr1 / NULLIF(table2.nr2, 0) as percentage
我想用关系代数来写这个。
可以用关系代数表示算术除法吗？
根据this course of the University of Rochester关系代数可以定义为
a formal system for manipulating relations
- Operands of this algebra are relations.
Operations of this algebra include the usual set operations (since relations are sets of tuples), and special operations defined for relations
selection
projection
join
这是一门关于关系的代数，没有数字的表示。如果你想对数字使用算术，你必须使用扩展的形式主义，例如 Safe Database Queries with Arithmetic Relations.