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7
votes
1answer
94 views

Functional dependencies applies to whole database or to a particular relation?

I am new to dbms. I saw a lecture video about functional dependencies. But I am confused a bit that whether functional dependency is a constraint put on whole database or on a particular schema?
6
votes
4answers
1k views

What exactly is overlapping candidate key?

Can some one please explain to me in simple terms what is overlapping candidate key ? What is overlapping as the name suggests? Consider the below relation R(L,M,N,O,P) { M -> O NO -> ...
5
votes
1answer
2k views

What permissions are needed to view dependencies?

My company is moving to a much more restrictive security model in the near future. As part of that we are changing specific servers to the new model and testing all our existing processes. One of ...
3
votes
2answers
1k views

Why is this relation in 3NF?

I have a relation: R4 = {{T,U,V}, {T → U, U → T, T → V}} I know from looking at the answer key that this relation is in BCNF. I'm going through the process of rigorously determining what normal ...
3
votes
1answer
314 views

Drop partition scheme with orphan indexes

I have a partition scheme in my SQL Server database that I am trying to drop. This scheme was used by 2 indexes, which I deleted. I can't delete the scheme, since it appears to still be used by the ...
3
votes
1answer
97 views

How can I prove / disprove If A ↠ BC and A → B then A → C

/ From GATE 2007 IT: Consider the following implications relating to functional and multi valued dependencies given below, which may or may not be correct. A) If A ↠ B and A ↠ C then A → BC B) ...
3
votes
2answers
580 views

multivalued weak key in ER database modeling

I was wondering since i didnt find out any clarification for this. I want to store movies that exist in different formats (dvd, bluray etc) and the price for each format differs from each other as ...
2
votes
1answer
91 views

How to find out if anything is running as or relies upon a user account in anyway before removing it?

Running SQL Server 2008. So I need to get around to removing an old users account, but I'm worried that just disabling or deleting it right away might cause some things to stop working properly if ...
2
votes
2answers
132 views

Relations, dependencies and normal form

I have some issues in understanding about relations and dependencies. I will show two examples and what I want to know: Assume the relation GTX {G,T,X} with the following dependencies: G,X -> T ...
2
votes
1answer
127 views

If A and B are candidate keys, then AB is candidate key or not ?

If R{abc} is a relation, f{ a->b b->a a->c b->c }, then a and b are candidate keys. What about ab ? Is it a candidate key or is it a super key or both ?
2
votes
1answer
21 views

Determining Transitive Dependencies

I am working on figuring out partial and transitive dependencies. The Transitive ones are really confusing me because I can see a transitive dependency on nearly all of these. The partial ...
2
votes
0answers
75 views

Is the table in 3NF?

I am creating a relational database - a library management system. I want to show an example where I normalize the data from 2NF to 3NF. My example of 2NF looks like The definition of third normal ...
2
votes
0answers
141 views

Identifying functional dependencies

I'm having trouble understanding the logic in use for identifying functional dependancies. Looking at the sample relation below, I understand fd1 - fd3. But when I look at fd4 and fd5, its logic ...
1
vote
1answer
247 views

How to include in the result of a `SELECT … GROUP BY …` all the other columns that are functionally dependent on the grouping ones?

I'll base this question on a toy example. Let this be table A: A ------------------------- U | V | W | X | Y | Z ------------------------- a | b | c | 1 | 6 | 8.3 a | b | c | 1 | 4 | ...
1
vote
2answers
356 views

PostgreSQL : dependencies on a schema

I need to delete a schema in my PostgreSQL database. I would like to make sure that the schema is not used in another schema (for instance : this schema is used for a view in another one). Is there a ...
1
vote
1answer
38 views

Apply Definition of MVD (multivalued dependency) to Example?

Supposedly this multivalued dependency (MVD) and this functional dependency (FD): {W} ↠ {N,D} and {W} → {N} hold in this table: V W N D ================= | v | w | n | 1 | ...
1
vote
1answer
244 views

Decompose table into third normal form

Tables X and Y are given as below : X (A, B, D, E, F, G, H, J) with A and B as primary key Y (K, L, M, N, O, P, Q, R) with K and L as primary key Now we need to decompose these tables into tables ...
1
vote
1answer
172 views

Optimizing bulk update performance in Postgresql with dependencies

Basically my question is the same as this one, but WITH dependencies, so drop/renaming the table is not a trivial option (I assume). We are refactoring a large, poorly designed table which has many ...
1
vote
1answer
82 views

all tables used by a stored procedure and all sps that use a particular table - recursive cte

I am working on a script that gives me a list of tables that use a specific stored procedure. It also works on all tables used by a stored procedure. on the example below, all stored procedures that ...
1
vote
0answers
44 views

testing an extraneous attribute in a relation using functional dependency

I am studying the book "Database System Concepts" by sudarshan . In chapter 8.4.3 in a dependency alpha->beta , If A ∈ aplha to check if A is extraneous, let (gamma = alpha − { A}), and check if ...
1
vote
0answers
153 views

SQLServer dependency graph and performance

I have a large stored procedure running on SQLServer2008 to produce a report on the previous day's data. It rehashes data from 12 tables, including a lot of ORDER by date and CASTS. Among others, it ...
0
votes
1answer
27 views

Relation in 2NF with a transitive dependency?

Tomorrow I have my final exam of Database Design but I have a doubt about the Second Normal Form (2NF). The definition says a relation is in 2NF if no non-prime attribute is partially dependent on a ...
0
votes
1answer
156 views

Find the functional dependencies that hold in a relation

There is a question in my book that asks the following: Suppose we have relation R ( A ,B ,C ,D ,E ) , with some set of FD’s, and we wish to project those FD’s onto relation S(A, B, C). Give the ...
0
votes
1answer
37 views

Dealing with co-dependent not null columns

Say I have a table entities (subclassed by people and organizations tables), where each entry requires a primary_email_id. The entities table looks like this: entities ======== id INT AUTO_INCREMENT ...
0
votes
1answer
4k views

Converted ERD into Dependency Diagram 1NF, 3NF

Thats the ERD. I'm studying for an upcoming test and having trouble getting my head around converting thes ERDs into dependency diagrams. This is from a previous exam that the Lecturer told us to ...
0
votes
0answers
42 views

Exam question about BCNF

I am trying to unravel the following question about BCNF from a past exam paper that is available online. The question, which is on page 7 of the linked PDF, says: Suppose that R(A,B,C,D) is a ...
0
votes
0answers
17 views

Determining the 3NF based on functional dependencies

Given a relation R = {E M L T} and functional dependancies LT -> E, ET -> L, TM -> E, and E -> M , I know that the superkeys of this relation is TL, TE, and TM. For 3NF, the left hand dependancies ...
0
votes
0answers
52 views

Creating objects containing collections of themselves

I'm creating a simple data structure using PL/SQL to help me work with some rows in tables which have dependencies upon each other. In short, I'd like to be able to create a graph using any ...
0
votes
0answers
21 views

Managing View Dependencies

I am using PostgreSQL and I am adding a single column to a view. Unfortunately, I will have to drop and recreate that view as well as the 9 other views that are dependant on the view. What ...
0
votes
1answer
31 views

Determining Functional and Transitive dependencies from Relational Model (with no sample data)

I have a relational model which I've converted from an EER diagram... I've been asked to find the functional and transitive dependencies but how does one do that when there's no sample data to start ...
-5
votes
1answer
87 views

Listing column dependencies

I want to alter the datatype of a table column from varchar(x) to varchar(y). To do that, I need to know what dependencies there are on this column. Any suggestions?