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Division in relational algebra

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Author: User
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The Division in relational algebra is not very explicit. Now, if you understand it, write it!

First, you must understand when division is required and what is the role of division?

1. Division is to find the entity in the relationship between two entities. Some attributes of the Division set are the real subset of the Division set. For example, in R ÷ s, an attribute in the property set of set S is the true subset of the Set R attribute set.

2. Assume there are R, S, and their relational set Rs. The meaning of RS ÷ S is to query the r tuples related to all tuples in S in the r-s relationship Rs.

Five basic operations in relational algebra: Sum, difference, Cartesian Product, selection, and projection. In my opinion, compared with the set, selection (horizontal) and projection (vertical) are unique processing methods in the orders table.

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Related Keywords:
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