# Tagged Questions

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### Question about cost optimization formula for SELECT

I am a student in computer science and I have a question, which refers to cost optimization. I have to read the book (Fundamentals of Database Systems from Elmasry and Navathe) and try to present the ...
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### what does “\” symbol mean? [closed]

I am new to database learning and came across this \ symbol. I googled but couldn't find what it meant. It was used in the context Q = R\S, where Q, R, and S are relations. (The = sign here means "...
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### Grouping operator in DBMS (γ) is duplicate-impervious. Why?

I'm reading Database Systems by Ullman where its mentioned that γ is duplicate-impervious. I don't understand why a simple group operation should cause elimination of duplicates. Aliter, Duplicate-...
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### Minimal 3NF normalization issues

I'm trying to learn how to normalize to 3NF but the example that my teacher gave us doesn't really help. The algorithm I always used is this one: Find a canonical cover F_c for F For each FD X->Y ...
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### Why are multivalued dependencies named that way?

I'm doing a relational design course on Stanford open courseware. I understand why functional dependencies are named that way - A->B means B is specified when A is specified, or in other words, the ...
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### What is stable history in a database?

I am reading the paper Making geo-replication fast as possible, consistent when necessary by Li et al. in which they propose a geo-replication system called "RedBlue Consistency". They have a table ...
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### Can there be situations where using (noexpand) on an indexed view is undesirable?

From the past experience using the schema bound and indexed view in a query with (noexpand) hint usually dramatically improves performance if the view is designed well. Apparently using the indexed ...
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### Tuple calculus: unsure if my reasoning is correct

I'm currently working through a tuple calculus question and I ran into a situation where I have two answers that seem correct to me and I am unsure if my logic is wrong or if they are both correct ...
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### Time complexity of query optimizer

I'm reading this article "How does a relational database work"(http://coding-geek.com/how-databases-work/) I'm confused by the section: Dynamic programming, greedy algorithm and heuristic. Using ...
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### What are the practical uses for relational calculus?

In my Database Design course we are learning both Relational Algebra and Relational Calculus. I can see where Relational Algebra could be useful since it is closely tied to SQL. Our professor said ...
310 views

### Do Nested Transactions commit? [closed]

I am not happy with the Wikipedia article about nested transactions. I would not use the word "commit" for a nested transaction. For me "commit" means "durability". A nested transaction does not ...
108 views

### Method to economically insert Bill of Materials BOM items into a Stock Table?

I’m new to the wonderful world of database design and I’m currently experimenting with an implementation for my little brother relating to Model Train Sets. [I will be using SQL Server 2012 / Asp.Net ...
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### Word for describing how normal (technical term) a database is

Database Normalization is the process of changing the structure of a formal database schema in order to minimize redundancy. Database theory describes some states of normalization in order to make ...
1k views

### Are junction tables a good practice?

Say I have a large table that holds the user's info and another table that holds several locations. Then I use another table that holds the user_id and the location_id. In order to retrieve the data ...
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### Canonical Cover for Functional Dependencies ho

I'm trying to decompose a relation into 3NF and I'm given the following information: Given R(A B C D E F G H I) Keys: {A,B} {A,D},{B,D} FDs: AB-> DE A->I B->CFGH G->H AD->BCEFGH BD-&...
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### Usage of non standardized queries

So this is more of a theory question than practical but I'd appreciate any help. My friend and I are doing a project to learn new stuff and have fun. He's a coder and I like to think that I'm good ...
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### Tuple Relational Calculus help? [closed]

I have the following three questions in relation to the following diagram: 1) How many copies of the book titled “The Lost Tribe” are owned by the library branch whose name is "Sharpstown"? {b....
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### Normalization to 2NF and 3NF

I solved this example to determine 2NF and 3NF. I would like to check if my answer is correct. Can somebody check the 2NF and 3NF of this example, please? R( A B C D E F G H I J) with functional ...
454 views

### Why is a functional dependency described as a “one-to-many” relationship?

As far as I know, the definition of a functional dependency reads that, given the attributes X and Y, "each X value is associated with precisely one Y value". But then the author of the article that I ...
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### Multidimensional aggregates

Suppose one wanted to cache simple aggregate data over a table or grouped parts of a table, one could simply make a table with the aggregated results. If the original table is only appended to, it is ...
131 views

### What's the term that describes filtering query that makes use of indexes

I am looking for a technical term that describes the type of query in SQL that makes use of indexes. I completely forgot the name and can not look it up anymore (there's even a Wikipedia article about ...
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### Database relationship refresher

All, After several years of programming applications, I'm looking to refresh my understanding of databases. What I knew to begin with was fairly basic, and honestly, it's disappeared over time. I ...
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### Simultaneous money withdrawls from a distributed/replicated database

Lets say I have \$10 in my bank account. The database is replicated in North America and Asia. At the exact same time I do a withdrawl of \$10 in N. America and in Asia, meaning that my withdraw would ...
336 views

### When should I use a new table?

If a database is to hold a large amount of eg tickets for concerts, should I make a new table for each concert, then keep a table connecting venues with concerts? I would like each ticket ID for ...
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### TRC: Select an ID if it appears on all measurements

I have these two "tables": Station (station_id, city) // Stations details Rainfall (station_id, date, amount) // Rainfall measurements With Tuple Relational Calculus (TRC), I need to ...
195 views

### Boyce-Codd Normal Form

I am bit confused with BCNF and would appreciate any clarification. I have a table The primary key is a composite of all its attributes. Is this table in BCNF? My assumption it is not, because ...
1k views

### Get the value of one attribute from the reference key of another table?

I have two tables named as ps_order_detail and ps_product_lang in MySQL. I want to get the product name from one table whose reference key is in another table. I have two tables. First the ...
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### Why does data get corrupted in “large” text files - Reasons to use database

I am just starting to learn about databases and using mysql. I read that databases are more reliable than having large ascii text files and that ascii text files are more prone to corruption as they ...
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### Decomposition of a relation to 2NF and 3NF

I am trying to solve this example, but for now I can't. Can somebody show me, step by step how to decompose this to 2NF and then to 3NF? R = {ABCDEF, ABC -> EF, B -> E, E -> D} key of this ...
3k views

### Find the highest graded student, using Tuple Relational Calculus

Suppose I have a table of students, containing their ID and their grade: ----------------- | id | grade | ----------------- | 1 | 83 | | 2 | 94 | | 3 | 92 | | 4 | 78 | ...
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### What does <> mean in Relational Calculus?

I saw a Tuple Relational Calculus formula, and it contained the symbol <> I couldn't find any reference to it anywhere - can anyone tell me what this means? (perhaps this question will be a ...
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### Database design implementing support for different languages [closed]

Today I was practicing database design, for example I was trying to build a database design where I would like to store my favorite shows. I have normlaised this database to the third form (at least I ...
176 views

### How to merge rows based on how much data they have?

I am cleaning data and I formed a table something like this: file | product | color | product_id --------------------------------------------- one.csv pipe blue null ...
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### Why add indexes to these columns in the Database?

I am trying to get my head around this code. It's from the Rails Tutorial Book and is part of the process of making a twitter like application. class CreateRelationships < ActiveRecord::...
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### Probable circular dependency, but query still runs

I built this ER diagram in MySQL Workbench and it will run and generate the database. My concern is that the relationship between the employees, departments, positions, and employment_statuses is a ...
440 views

### how to explain indexes

This question is about teaching: When I learned databases, we talked about indexes being like the card catalog in the town library. We had at least an author index, a title index, then the Dewey ...
541 views

### Relationship between professor and course [closed]

I'm designing a database where I have a Course table and and Professor table. The business rules are : 1) A professor can teach many courses. (This is obvious). However, I get stuck in the second ...
52 views

### Where should a default setting field be?

I am creating a database to track occurrences of incidents on buses based on an existing system. Currently the drivers can set a default bus number, which is used to pre-populate the bus number on the ...
589 views

### Database with insert data every 2 minutes

I have a site to develop into PHP and mysql where I take, with a cron, every two minutes 10 xml from a server parse each and insert data into my database. Well this data are simple string (maximum 10) ...
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### Why is LRU is not suitable for joining 2 relations in DBMS [closed]

In DBMS, can someone please explain how the LRU (least recently used) buffer replacement policy acts when joining 2 relations in a database? I have read that LRU is not efficient when joining two ...
101 views

### Approach for a 2,000 table migration

What might be the best approach when converting or migrating a database containing over 2,000 tables? Where would you begin to tackle such an issue? Steps to take in the first weeks of designing? ...
126 views

### Column partially determining accepted values of another column, should be somehow normalized?

I have a table that describes a set of properties (yes it's metadata, in this case there's a valid reason to have it in the database); among other things I tell the type of the data that can be ...
58 views

### Adding users to a list and sort by category?

I'm using SQL-Server 2012 and I would like to know how to solve this program. So: I want to create a page that allows admins to manage a project, and part of it, would be to add members/employees to ...
266 views

### Multiple instances in Oracle

I'm really confuse with the term instance and database. So, my first question is how database and Instance are related in Oracle, I mean, whether an instance is associated with one/multiple database(s)...
764 views

### Closure of attributes definition clarification

A databases book I am using states [1]: The closure of {A1, A2, ..., An} under the FD's in S is the set of attributes B such that every relation that satisfies all the FD's in set S also satisfies ...
360 views

### How can I move 5 GB data from one database to another faster?

I'm using MySQL as database with Windows server. I'm having 5 GB of data in database. Now I need to change my server and the question is that how can I transfer complete 5 GB data to one mysql ...
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### Examples of a database with no consistency measures that ensures consistency through schema alone

To clarify, the database can be any type RDBMS, NoSQL/BigTable. However, it must not employ any usual consistency measures such as locks, or synchronization, but the inconsistency-invincibility must ...
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### In DBMS binary relationship is better than ternary

For which reasons (Features/points) binary relationship is better than ternary one in Database ER modeling? I got something by searching in website but those are not precise and meaningful!