All Questions
Tagged with rdbms relational-theory
10 questions
10
votes
2
answers
24k
views
How to insert values in junction table for many to many relationships?
I have three tables in database:
trips(trip_id(pk), trip_name(unique), user_id(fk))
places(place_id(pk), place_name(unique))
trips_places_asc(trip_id(fk), place_id(fk))
Since many trips can ...
- 257
7
votes
2
answers
1k
views
Does the concept of candidate key exist only in theory?
I know the concept of candidate key in RDBMS theory, but do candidate keys really exist in actual SQL engines? I mean is there any way to designate a particular column or set of columns as a candidate ...
- 249
5
votes
3
answers
3k
views
Why Cassandra is not considered a relational database?
Read this answer
Relational databases are based on the relational model, an intuitive, straightforward way of representing data in tables. In a relational database, each row in the table is a record ...
- 169
2
votes
0
answers
183
views
Understanding multivalued dependencies
This is my first time studying multivalued dependencies and there is a question that was posted by my lecturer as a class exercise. I have an answer, but I'm not 100% sure it was right. Please let me ...
- 21
0
votes
2
answers
177
views
Need help about giving relationships in database design
I am developing a simple blog application in which users can write posts and others can like, comment, share etc. i am facing difficulty in designing database.
What I have tried is:
user (user_id(pk),...
- 257
0
votes
1
answer
52
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
0
votes
2
answers
450
views
Database: Splitting tables based on logically grouped optional columns
I keep having this argument with my management about splitting the tables. I prefer splitting a database table to multiple tables based on attributes that can be grouped together. The columns which ...
- 101
0
votes
2
answers
89
views
Multiple Primary-Foreign Key connections between Tables Redundant?
I have two tables, Reviews and Critic
I'm pretty new to RDBMS and I was wondering if the connection between Review.rID and Critic.Review is redundant?
My reasoning is that a single critic can have ...
-1
votes
1
answer
305
views
Help writing the following query to relational algebra
Can someone help me in writing the following query to relational algebra, I am studying DBMS and I am stuck on this exercise.
Query:
SELECT a.name, d.name. d.grade
FROM student a, enrolled i, class ...
-2
votes
2
answers
174
views
Why is it a bad idea to have multiple values in a column in a relational database?
One problem I've found is slow database queries. If I had a table that had a column titled customer and another column titled grocery_items that contained multiple grocery items, then a simple query ...
