Questions tagged [database-theory]
The database-theory tag has no summary.
121 questions
0
votes
0
answers
20
views
How to draw labeled precedence graph to test for view serializability?
Time | T11 | T12 | T13
--------------------------------------------
t1 | r(x) | |
t2 | | w(x) |
t3 | w(x) | |
t4 | | ...
- 101
0
votes
1
answer
135
views
Is that table in BCNF?
In the book I am currently reading this table is mentioned as an example for what we can do if a table fulfills BCNF but has still redundancies. It then mentions that a solution are arrays. But is ...
- 141
0
votes
1
answer
101
views
Is snapshot isolation only potentially different from serializability if there are "cycles" between transactions with reads and writes?
I'm trying to figure out a better intuition for what exactly are the sorts of consistency anomalies that snapshot isolation allows to happen. The description on Wikipedia says:
In databases, and ...
- 101
0
votes
2
answers
112
views
How do I identify the SQL server brand via SQL queries
A 3rd party API exposes a endpoint which accepts "SQL" queries. Their examples are simple SELECT statements, however I want to write more complicated queries.
They do not specify which SQL ...
- 101
-1
votes
1
answer
66
views
How do database snapshots work?
How do database engines take consistent snapshots when writes could be happening at any time?
(A) Does the database engine block writes one table at a time while taking snapshots?
(B) Does the ...
- 99
0
votes
1
answer
70
views
What does relational capabilities mean in Codd's Foundation rule?
From Codd's 12 rules (emphasis mine):
For any system that is advertised as, or claimed to be, a relational
data base management system, that system must be able to manage data
bases entirely through ...
- 131
1
vote
1
answer
171
views
Doubt on 2NF decomposition
I have read that 1NF, 2NF and 3NF decompositions are lossless and dependency-preserving.
Consider this example on a relation R(A,B,C,D) with functional dependencies set as FD ={ AB->CD, A->C, BC-...
- 11
4
votes
1
answer
242
views
T-SQL: Iteration vs. Set-Based Operations When Independence of Ancillary Data is Needed
BACKGROUND
I am using Microsoft SQL Server Management Studio v18.9.1 on Windows 10.
I've created a database to store test results of our company's widget (not yet being produced). I am working on a ...
- 197
1
vote
0
answers
98
views
Is there a formalism for the kinds of constraints we can implement with indexed-views? Or at least a rule-of-thumb?
SQL Server’s Indexed Views provide a performant way to implement certain classes of database-scoped constraints - such as ensuring a value is unique over multiple tables - or other non-key, cross-...
- 692
0
votes
0
answers
364
views
Weak Entity with Primary Key?
I have the following E-R diagram to refer to:
I have a question posed to me that entity 4 IS a weak entity due to one of its relations. However, from what I see, entity 4 has a composite primary key ...
-1
votes
1
answer
890
views
Why can't Many to Many relationships exist in relational database management systems?
While reading Oracle 11g Sql by Joan Casteel, the author mentions that many to many relationships couldn't exist in relational databases. I was wondering what the reasoning behind this fact was.
- 11
0
votes
1
answer
465
views
Why is SQL not considered a programming language?
If a database is just a computer system that implements a database management system, and we use SQL to tell it what to do, why don't we consider SQL to be a programming langauge?
From Wikipedia:
A ...
- 11
0
votes
1
answer
44
views
Convert generalization in ERD to Relationnal Database having no additional column
I've a quite simple problem but the litterature I came accross didn't seem to dwell on.
Let's say I have an entity OFFER which represents an Offer on a Product, for each product, one offer can be &...
- 1
3
votes
1
answer
1k
views
Compensation Log Records (CLR) in UNDO-Phase of Database Recovery
The compensation logs' redo-information corresponds to the undo-information of the log entry that made their creation necessary during the undo-phase.
That sounds to me like the CLRs redo information ...
- 33
1
vote
1
answer
199
views
Is COW (copy-on-write) based atomic commit widely used in mainstream databases?
The database is not a flat structure like a file system, and generally has three to four levels of index levels. If you simply use COW, you will have obvious write amplification every time you modify ...
- 111