select – 关系代数中的算术划分

我有一个SQL请求:

SELECT table1.nr1 / NULLIF(table2.nr2, 0) as percentage

我想在关系代数中写这个.

是否有可能在关系代数中表示算术除法?

最佳答案 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

它是关系的代数,没有数字的表示.如果你想对数字使用算术,你必须使用扩展形式,如Safe Database Queries with Arithmetic Relations.

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