3nf | 易学教程

SQL equivalent of IN operator that acts as AND instead of OR?

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问题 Rather than describe, I'll simply show what I'm trying to do. 3 tables in 3NF. product_badges is the join table. (The exists sub-query is necessary.) SELECT * FROM shop_products WHERE EXISTS ( // this line cannot change SELECT * FROM product_badges as pb WHERE pb.product_id=shop_products.id AND pb.badge_id IN (1,2,3,4) ); Now this will return all the products that have a badge_id of 1 OR 2 OR 3 OR 4. What I want is to get only the products that meet ALL those values . I tried to do pb.badge

Understanding 3NF: plain English please

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问题 I am working through an example problem in which we are trying to identify which of the following relations is in Third Normal Form (3NF). Here are the relations we are given: R1(ABCD) ACD -> B AC -> D D -> C AC -> B R2(ABCD) AB -> C ABD -> C ABC -> D AC -> D R3(ABCD) C -> B A -> B CD -> A BCD -> A R4(ABCD) C -> B B -> A AC -> D AC -> B I know the answer is R1 is in 3NF, but I'm having a hard time understanding the steps to go about determining what violates 3NF. Can

Understanding 3NF: plain English please

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Converting 3NF to BCNF when there is a circular dependency

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问题 If we have a relational schema R(A, B, C, D), with the set of dependencies: ABC -> D D -> A How is it possible to decompose R into BCNF relations? The only plausible way seems to be to discard one of the FDs, no matter how I think about it. Is there any other way? 回答1: That's right, one can always losslessly decompose to 3NF while preserving FDs but BCNF might not preserve them. Nevertheless it's a lossless decomposition: the components, if holding projections of the original, will join to

What is the difference between 3NF and BCNF?

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问题 Can someone please explain the difference between 3NF and BCNF to me? It would be great if you could also provide some examples. Thanks. 回答1: The difference between 3NF and BCNF is subtle. 3NF Definition A relation is in 3NF if it is in 2NF and no non-prime attribute transitively depends on the primary key. In other words, a relation R is in 3NF if for each functional dependency X ⟶ A in R, at least one of the following conditions are met: X is a key or superkey in R A is a prime attribute in

Database Normalization Process to 3NF CustomerRental for CustNo, PropNo, OwnerNo, etc

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问题 I am trying to normalize the following table. I want to go from the UNF form to 3NF form. I want to know, what do you do at the 1NF stage? It says it's where you remove the repetitive columns or groups (ex. ManagerID, ManagerName). This is considered repetitive because it's leads to the same data. The Unnormalized data table has the following columns CustomerRental(CustNo,CustName,PropNo,PAddress,RentStart,RentFinish,Rent,OwnerNo,OName) There are no repeating columns/fields and each cell has

Grails: Many-to-Many without hasMany/belongsTo - instead using native 3NF - Searching full text

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I am implementing a many-to-many mapping in grails using 3NF, Not using the hasMany or belongsTo property. Taken from this article it shows and explains quite a lot about its advantages. Article: http://burtbeckwith.com/blog/?p=169 Presentation notes: http://burtbeckwith.com/blog/files/169/gorm%20grails%20meetup%20presentation.pdf I'm trying to make a Tag system onto questions, kind of like this(stackoverflow :)) I can save the Question and the Tags, then save the association with them, but now I want to be able to search and serve up a full Question with Tags, I have 3 domain classes -

Deciding whether a relation is 3NF or 2NF

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From the Database Management Systems book: given the relation SNLRWH (each letter denotes an attribute) and the following functional dependencies: S->SNLRWH (S is the PK) R->W My attempt: First, it is not 3NF: for the second FD, neither R contains W, nor R contains a key, nor W is part of a key. Second, it is/not 2NF. If we examine the second FD, W is dependent on R, which in turn is not part of a key. STUCK. 2NF is violated if some proper subset of a candidate key appears as a determinant on the left hand side of one of your (non-trivial) dependencies. Ask yourself whether any of your

Normalization of an 1:1 or 1:0 relationship

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when using relation databases and you want 3NF (do you call it 3NF in english?), then you pull 1:1 relationsships together into one table. But what happens if the rationship is 1:0/1 (/ meaning or)? Then you keep them separated to avoid blank spaces in tables? Kepping them apart is valid 3NF in ths case? Third normal form basically means that an attribute (or column) depends on the key, the whole key and nothing but the key (so help me, Codd). If you have an attribute which is either there or not there, that attribute itself may still follow the rules. In those cases, I would simply keep the

Normalization of an 1:1 or 1:0 relationship

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问题 when using relation databases and you want 3NF (do you call it 3NF in english?), then you pull 1:1 relationsships together into one table. But what happens if the rationship is 1:0/1 (/ meaning or)? Then you keep them separated to avoid blank spaces in tables? Kepping them apart is valid 3NF in ths case? 回答1: Third normal form basically means that an attribute (or column) depends on the key, the whole key and nothing but the key (so help me, Codd). If you have an attribute which is either