Questions tagged [databases]
The databases tag has no usage guidance.
-1
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0answers
3 views
What is the time complexity for SQL Insert Statement? [on hold]
I am doing SQL Insert Statement. May I know:
What is the time complexity for SQL Insert statement?
Does O(m x log(n)) consider as time complexity for SQL Insert Statement?
What is the best case and ...
0
votes
0answers
13 views
Analysing data from amazon textract - python [closed]
I am creating a piece of software for my company where I need to check the math on invoices we receive from companies. The pdf invoices vary from 20-100 pages. The invoice we receive from each company ...
1
vote
1answer
25 views
In a DBMS what are the implementation details that make set operations faster than cursors?
What are the low level implementation details that make set based operations exponentially faster than iterative processes, like cursors?
At a memory level how does a set operation "touch" the data ...
1
vote
1answer
18 views
Adding an ordered into a relationship without violating the functional dependencies
Assuming that we have the relationship $R(A,B,C,D)$, the tuple $(W,X,Y,NULL)$ and the following functional dependencies:
$$A \to C$$
$$A \to B,D$$
is it possible to insert a tuple with $NULL$ values,...
1
vote
1answer
21 views
Find candidate keys given functional dependencies
In my database class we practiced how to find the candidate keys, given the functional dependencies. However they were easy examples, based on a single attribute being functionally dependent on a ...
1
vote
1answer
37 views
How to find highest normal form of a relation, given its functional dependencies
Let's say that I have a relational model, defined as:
$$X(A,B,C,D,E,F,G)$$ with the functional dependencies:
$$f_1: \{A,B,C\} \to \{D,E,F,G\}$$
$$f_2: \{A,B\} \to \{C\}$$
Using this information I ...
0
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0answers
17 views
Need an optimized way to handle combination of entities to improve performance
So, I am working on a feature in a web application. The problem is like this-
I have four different entities. Let's say those are - Item1, ...
0
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0answers
20 views
Doubt on Lossless or Lossy Decomposition
Consider a relation $R\left ( A,B,C,D,E \right )$ and functional dependencies are
$F=\left \{ AC\rightarrow B,C\rightarrow D,A\rightarrow E,C\rightarrow B \right \}$
Relation $R$ is decomposed into ...
0
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0answers
12 views
Doubt on the definition of Partial funtional dependency
I have some doubt regarding the definition of partial functional dependency.
According to the book Fundamentals of Database Systems by Elmasri and Navathe
the definition of partial functional ...
2
votes
1answer
115 views
Why do OS and DBMS have their own synchronisation mechanisms, when OS can alone do it and it sits at the bottom of DB?
I know that synchronization is important in the OS, but why do we need a separate topic synchronization and concurrency in the DBMS? The OS concentrates on program synchronization while the DBMS ...
0
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0answers
26 views
Relational Database to Aggregate Data Model
Can any application currently using a relational database be rewritten to use an Aggregate Data Model, by Focusing on data modelling aspects only (ignoring other features like salability or ...
1
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0answers
28 views
How do I implement fixed block storage file system in database from typical file-level file system?
I've a typical parent ID based file system in database and files are physically stored on disks. What I want is to store files in blocks (4096K) of fixed size.
Chunking can be used I found, but how ...
0
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0answers
20 views
Understanding non repeatable read anomaly in databases
This paper discusses in detail ANSI isolation levels discussed in ANSI SQL standard on page 84.
Paper introduces following shorthand for describing histories which contain reads, writes, commits and ...
0
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0answers
39 views
When cascadeless and / or recoverable schedules can contain blind writes?
Some quick definitions / theory:
If instructions $I_i$ and $I_j$ of two different transactions operate on same data item and if any of them is a write operation then they are conflicting ...
1
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0answers
16 views
Understanding connection between different database concurrency control protocol
I have came across following diagram related to timestamp based concurrency control protocols in database systems:
I don't know whether its correct or not.
As per my interpretation, it means all ...
1
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0answers
25 views
Understanding validation based database concurrency control protocol
Database book by Korth explains validation protocol as follows :
To perform the validation test, we need to know when the various phases of transactions took place. We shall, therefore, associate ...
0
votes
1answer
68 views
Why “ every non-prime attribute of R is non-transitively dependent on every key of R” in the original def of 3NF?
I have read the definition in of Third_normal_form here
, which shows
The third normal form (3NF) is a normal form used in database normalization. 3NF was originally defined by E.F. Codd in 1971.[2]...
1
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0answers
23 views
Why don't RDBMS use a quorum based solution to do failover
For RDBMS viz. MySql, PostgreSql a common solution for scalability and high availability is to run a primary instance as master that is a read-write instance and one or more read replicas. If the ...
0
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1answer
45 views
Doubt regarding foreign key and referential integrity
I am studying database from Database System Concepts.
The author was explaining foreign keys and referential integrity with the help of following schemas:
$$ instructor(\underline{ID},\space name,\...
0
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0answers
8 views
view serialisable and conflict serialisable
I recently was solving some problems on these topic and realised that in cases where conflict serialisable schedule existed; the number of view serialisable schedule was actually equal to the number ...
0
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0answers
53 views
When BCNF decomposition preserves Functional Dependencies?
It is known that BCNF decomposition does not preserve functional dependencies (FDs). For example, for FDs on R(A,B,C),
...
0
votes
3answers
78 views
Functional Dependencies
Let relational schema R(A,B,C,D,E,F,G,H,I).
The functional dependencies are: A -> BC, AD -> BE, C ->F , A->F , D-> E
Find the number of non-trivial functional dependencies ? I know that R has only ...
0
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0answers
74 views
How are these two definitions of the Third Normal Form (3NF) equivalent?
According to the textbook by Silberschatz,
A relation schema R is in third normal form with respect to a set $F$ of functional dependencies if, for all functional dependencies in $F^+$ of the form $\...
0
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0answers
75 views
Any Recoverable schedule which is not a Cascadeless schedule?
When I read about Cascadeless schedule, it says "Every Cascadeless schedule is also recoverable schedule." and the examples are also almost same. I want to know an example of Recoverable schedule ...
0
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0answers
10 views
Is a schedule with autocommit and no aborts automatically recoverable?
As in the title, since we won't have problems with cascading aborts and each transaction is committed automatically, doesn't this mean that the schedule will always be recoverable?
0
votes
1answer
29 views
Given a relation and asked to enumerate all FD's and mark the trivial FD's
Given a relation R(A,B,C) and a FD set (A->B, B->C), find the FD Closure. Enumerate all the FD's and organize them accordingly to the LHS of the FD's. Mark all the trivial FD's.
I am a little ...
0
votes
1answer
21 views
Maximum join of relations
I have a question as follows
Consider the relations $r1(P, Q, R)$ and $r2(R, S, T)$ with primary keys $P$ and $R$ respectively. The relation $r1$ contains $2000$ tuples and $r2$ contains $2500$ ...
0
votes
1answer
74 views
How to decompose into BCNF while preserving all functional dependencies
I have a relation R = {A,B,C} and F={AB -> C , C -> B}.
In order to check if R is in BCNF.
I checked if AB and C are both superkeys and since C is not a superkey I conclude R is not in BCNF.
After ...
1
vote
1answer
86 views
Is my decomposition of R into 3NF is lossless and preserving all dependencies?
I have a schema R = {A,B,C,D,E} and the set F of FDs:
F = {A --> BCDE, CD --> E, EC --> B}.
Candidate key = A
Non - Prime Attributes = BCDE
Prime Attributes = A
According to me, there is no partial ...
0
votes
1answer
38 views
Did Date and Darwen's “Third Manifesto” have a lasting impact?
In 1995, two DB theory researchers, C.J. Date and H. Darwen, published a text with the rather impressive-sounding name "The Third Manifesto" with their ideas regarding future DBMSes, which would ...
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2answers
269 views
Is it possible to do a NULL comparison in Relational Algebra?
Please consider the following question given in a booklet:
I have read about databases from Database System Concepts - by Henry F. Korth, but never saw an instance where we could do a NULL comparison ...
1
vote
1answer
59 views
Raft algorithm: What's the data format of `term`?
Time is divided into terms, and each term begins with an election. After a successful election, a single leader manages the cluster until the end of the term. Some elections fail, in which case the ...
1
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0answers
67 views
How to determine conflict serializability without read and writes
I'm learning about conflict serializability in an introduction to databases class. I know how to check if a schema of transactions is conflict serializable when there's reads and writes. Draw the ...
1
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0answers
26 views
normalization: how does nf work?
I once did normalization for my Computer Science project, and I had to turn 0NF to 1NF, 2NF and 3NF.
What must we actually do to convert 0NF to 1NF, 2NF and 3NF? Must we rearrange the information and ...
1
vote
0answers
22 views
Merge unstructured with structured data
We have a database with well-formated and structured data. From time to time we get Excel - files from our clients. This Excel Files have to be imported to the database. It it very important that we ...
-2
votes
1answer
36 views
How to find information quickly in a table
I have a table and asked me to add my information to it. And then asked me to find my information in the easiest way (after adding your details to the table, assume that the table is arranged ...
0
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0answers
92 views
How is Eventual Consistency (EC) better than Strong Consistency (SC) when N = 3, R=W=2 when SC gives better consistency gurantee in same config?
In dynamo paper, it says that in production most of the users set N = 3, R = 2 and W = 2.
...
0
votes
1answer
80 views
Where do you exactly use data structures?
I know what data structures is, How it works & importance of it. I just have some doubts on where do we actually use it.
When database can do filtering, fetching, sorting efficiently, Why we ...
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2answers
244 views
How many candidate keys are there in the table shown below?
One candidate key is (report_no, author_id).
What are the other candidate keys?
0
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1answer
54 views
Checking claim in paper “A Read-Only Transaction Anomaly Under Snapshot Isolation” by Alan Fekete et al
In the 2004 paper "A Read-Only Transaction Anomaly Under Snapshot Isolation" by Alan Fekete et al. (which can be found here and here) the authors state:
We also note that any execution of T1 and T2 ...
0
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1answer
60 views
What are the essential differences and similarities among “data”, “Information” and “knowledge” in the context of Computer Science?
The terms "data", "information" and "knowledge" are quite interchangeably used in Computer Science. Strictly speaking, they do carry a very different meaning. I want to know their precise meanings and ...
0
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1answer
28 views
Is relation following given characteristic already in 2NF, 3NF and BCNF?
The definitions of 2NF, 3NF and BCNF goes like this:
2 Normal Form (NF) definition
A relation is in second normal form if and only if it is in first normal form and all the non-key attributes ...
0
votes
1answer
120 views
Use of existential quantifier in tuple relational calculus
It is somewhat confusing to me when to use quantifiers in tuple relational calculus (TRC). I stumbled upon following problem and I am still scratching my head thinking why not TRC query can be ...
-2
votes
1answer
129 views
Query Super Type and Subtype in Mysql
Assuming I have a schema depicted in the image , showing relationships(specialization) between Staffs, Academic Staffs and Non Academic Staffs. Is it possible to have a query that retrieves the ...
0
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0answers
105 views
Data structure for a single elimination tournament and its implementation
I want to implement a tournament managing software , something like challonge(https://challonge.com/) and am currently stuck at the data structure to be used. I read up on tournament trees and a ...
0
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0answers
78 views
Databases - How to generalize an sql query from a specific input? find project number, number of employees
Schema:
http://comet.lehman.cuny.edu/jung/cmp420758/DBMidexamFa14-SelectedSolution.pdf
Write SQL code to find the following details:
For each project: find the project number and the number of ...
2
votes
1answer
84 views
Fastest way to search a word in a word list?
I have a word list like "English Open Word List" used to create word games.
The list is in txt file with space between words, like;
aa
aah
aahed
.........and so on.
I want to search it while typing ...
4
votes
0answers
33 views
Any elegant approach to search where users have permissions on subset of records?
I work in Search and have seen following problem appear in different forms. There are many users in an enterprise; they have ability to create records. Each user has variable level of access to some ...
-1
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1answer
141 views
What is the equivalent form of full outer join in relational algebra?
Considering only basic relational algebra operations, how can we implement the full outer-join ?
2
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1answer
87 views
How to do compare-and-increment different locations with in memory MVCC?
I'm reading the paper An Empirical Evaluation of
In-Memory Multi-Version Concurrency Control which is about implementations of MVCC for in-memory databases. Section 3.3 on Two-phase Locking (MV2PL) ...
