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Tagged with relational-algebra aggregate-functions
11 questions
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How to add virtual column in relational algebra
Suppose we have table A and a table B which has foreign key referencing A's PK.
The following query in SQL selects all rows and columns of A and an aggregation (for example SUM) of Bs for each row of ...
- 357
1
vote
0
answers
1k
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Relational Algebra using aggregate functions?
I have written a couple of queries using aggregate functions and since I cannot check them using winRDBI, I would like to ask if I did them correctly?
Below is the database schema:
Author - (...
- 419
0
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0
answers
308
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Relational algebra - SQL MAX per value
I am making up exercises for myself and stumbled across this question:
Given this example relation:
Person(name, birthyear)
Find the relational algebra expression to find the youngest person per ...
- 381
-1
votes
1
answer
178
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Relational algebera without aggregate functions
The table WORKING has the names of students and projects.
The values are:
(s1,p2)
(s1,p3)
(s1,p4)
(s2,p3)
(s2,p4)
(s3,p1)
(s4,p1)
(s3,p2)
(s4,p2)
(s5,p3)
(s5,p4)
(s6,p3)
I have to find the pair of ...
user5439550
0
votes
5
answers
1k
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Relational algebra without aggregate function
We have a table Phone whose values are
(Name, Number)
--------------
(John, 123)
(John, 456)
(Bravo, 789)
(Ken, 741)
(Ken, 589)
If the question is to Find the guy who uses only one number, the ...
- 1,608
-2
votes
2
answers
680
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Relational algebra operations [closed]
I'm stuck with relational algebra.
I mean, how can I express functions like "SUM(), COUNT()," etc in RA?
Thanks, any help will be kindly appreciated
- 92
1
vote
1
answer
4k
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Query in relational algebra without using aggregate functions
Task from exam for subject Database Systems:
I have following schema:
Excavator(EID, Type) - EID is a key
Company(Name, HQLocation) - Name is a key
Work(Name, EID, Site, Date) - All collumns ...
- 177
2
votes
1
answer
2k
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Query using aggregation and/or groups in relational algebra - count, max, min, etc
I have read much in textbooks and browsed a lot of pages on the internet but I can't understand how functions/operators like min, max, count, ... that aggregate over a relation/table or groups of ...
- 181
0
votes
1
answer
2k
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compare an attribute value to the value of an aggregate function in relational algebra
How can one compare an attribute value to the value of an aggregate function in relational algebra?
Something like:
SELECT [attribute1 > COUNT(attribute2)] (relation)
My teacher is a stickler on ...
- 83
0
votes
1
answer
1k
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Relational Algebra using winrdbi - count
i am studying relational algebra and i am using winrdbi to check if my queries are correct
i am trying to get the count from a colum like this:
q1:=count(tr_numb)(tree)
however i keep getting an ...
- 781
24
votes
5
answers
22k
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Aggregate Relational Algebra (Maximum)
I am currently working on a homework assignment that requires a selection to occur that pulls out an element containing a specific attribute of maximum value compared to all other records. I've read a ...
- 2,755