learn relational algebra

1. Introduction to relational algebraRelational algebra is an abstract query language and a traditional expression of relational data manipulation language. It expresses queries by relational operations. The calculation object of relational

Relational Algebra Q: Why is it called algebra? A: Because there are operators and operands, the operand is a table, the operator is the intersection, and so on; Relational algebra is divided into set-based relational

era is not easy to deal with. You're faced with a plethora of users who want to provide continuous service to a wide range of users in the cloud.Second, the separation of . Data in different times and places is separate, and data management requires federalism, not unitary. For example, Beijing's data, below the Haidian, Chaoyang these, but you want to replace Hebei province, the middle of a layer of Shijiazhuang, Baoding these cities, the level is not the same, not to make them into the same d

limit is 1 million lines, but flexible analysis when users often do not have that large amount of data.The OLAP system, which is traditionally modeled, is like a cumbersome train model that runs much faster, but is too rigid. and users need more flexible car mode, I do not need to pull so much to run so fast, I need to go where I want to go.We look at Excel, I don't care about its formatting ability, is not able to make a good-looking report out, I only care about its ability to calculate the d

Algebraic operations of five basic relationshipsCollection : Some specified sets of objects together become a collection in which each object is called an element.The three characteristics of a set: certainty, reciprocity, and disorder.(1) Certainty: Refers to a clear concept, the object description is clear, can not be vague, not ambiguous.(2) Cross-anisotropy: for a given set, any two of its elements are different.(3) Disorder: Given a set, the relationship between the elements in the set can

small for the standard change) Step three: Look at the b→c, similar to the second step. ...... The following: De→c is the same. Another method: If R is decomposed into a function-dependent set satisfied by P={r1,r2},f R, the sufficient and necessary conditions for the decomposition p to be lossless are: The r1∩r2→ (R1-R2) or r1∩r2→ (R2-R1) ps:-operation is made up of the public properties of R1 and R1 that are removed from R2. Relational

Copyright Notice The architecture Architect's tutorial, "The 4th edition" of the architect's exam, is the author of the "School of soft test for Greek games". Complete the relevant reading notes for later self-examination, only for personal learning and use, not for any commercial purposes. Copyright Notice Fourth section relationship algebra and differential Cartesian product projection theta Connection apart fourth section

the relationship s. Compare to discover:The X1 image set is only Y1 and cannot contain all the values of the attribute y in the relationship s, so the X1 is ruled out;And X2 's image set contains all the values of attribute y in relation s, so the r÷s end result is X2,Maybe now you know a little bit about how the division operation is done, so let's take a look at what the division can solve.Take a look at the following small example:With relationship R,s and RS, for rs÷s resultsIt's easy to ge

first, the traditional set operation and SQL statement implementationthe traditional set operations include four operations: and (∪), intersection (∩), Difference (-), Generalized Cartesian (X). and Operations (Union)the corresponding SQL statement:SELECT * FROM R Union select * from S; intersection operation (Intersect)the corresponding SQL statement:SELECT * FROM R Intersect select * from S; difference operation (Except)the corresponding SQL statement: SELECT * from R Except select * from

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 tr