How to find the maximum in relational algebra?
$begingroup$
This is my database course's homework.
We have this relation.
Trained(A, B) A trained B
How can I figure out who has trained the most people by using relational algebra or it cannot be expressed in relational algebra?
for example,
(John, Kenny)
(John, Kei)
(John, Cohen)
(Willson, John)
(Kenny, Peter)
(Ho, Tina)
In these tables, the answer obviously is John.But is it possible to express in relational algebra?
relation-algebra
asked Oct 10 '16 at 0:40
JohnJohn
24
$endgroup$
add a comment |
$begingroup$
This is my database course's homework.
We have this relation.
Trained(A, B) A trained B
How can I figure out who has trained the most people by using relational algebra or it cannot be expressed in relational algebra?
for example,
(John, Kenny)
(John, Kei)
(John, Cohen)
(Willson, John)
(Kenny, Peter)
(Ho, Tina)
In these tables, the answer obviously is John.But is it possible to express in relational algebra?
relation-algebra
asked Oct 10 '16 at 0:40
JohnJohn
24
$endgroup$
add a comment |
$begingroup$
This is my database course's homework.
We have this relation.
Trained(A, B) A trained B
How can I figure out who has trained the most people by using relational algebra or it cannot be expressed in relational algebra?
for example,
(John, Kenny)
(John, Kei)
(John, Cohen)
(Willson, John)
(Kenny, Peter)
(Ho, Tina)
In these tables, the answer obviously is John.But is it possible to express in relational algebra?
relation-algebra
asked Oct 10 '16 at 0:40
JohnJohn
24
$endgroup$
This is my database course's homework.
We have this relation.
Trained(A, B) A trained B
How can I figure out who has trained the most people by using relational algebra or it cannot be expressed in relational algebra?
for example,
(John, Kenny)
(John, Kei)
(John, Cohen)
(Willson, John)
(Kenny, Peter)
(Ho, Tina)
In these tables, the answer obviously is John.But is it possible to express in relational algebra?
relation-algebra
relation-algebra
asked Oct 10 '16 at 0:40
JohnJohn
24
asked Oct 10 '16 at 0:40
JohnJohn
24
asked Oct 10 '16 at 0:40
JohnJohn
24
asked Oct 10 '16 at 0:40
JohnJohn
24
asked Oct 10 '16 at 0:40
JohnJohn
24
24
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
You use GROUP and HAVING. I don't know how your class does notation, but in mine we do something like this:
SELECT A FROM Trained GROUP BY A HAVING COUNT(A)
I'm not sure if this is correct, but it should be similar.
answered Oct 23 '16 at 16:56
user1766555user1766555
3092618
$endgroup$
add a comment |
$begingroup$
Yes, it is possible to express it in relational algebra (RA).
The following line groups column A by COUNT(A). And plots COUNT(A) as 'frequencyOf_A'.
γ A; COUNT(A)→frequencyOf_A (Trained)
Resulting in this:
Trained.A frequencyOf_A
John 3
Willson 1
Kenny 1
Ho 1
I used this RA engine. And uploaded your relation via github's gist. Thanks. (On the side "relation algebra" is mathematics, while "relational algebra" is considered computer science I think.)
answered Oct 17 '17 at 23:44
Petr KosvanecPetr Kosvanec
11
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add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
You use GROUP and HAVING. I don't know how your class does notation, but in mine we do something like this:
SELECT A FROM Trained GROUP BY A HAVING COUNT(A)
I'm not sure if this is correct, but it should be similar.
answered Oct 23 '16 at 16:56
user1766555user1766555
3092618
$endgroup$
add a comment |
$begingroup$
You use GROUP and HAVING. I don't know how your class does notation, but in mine we do something like this:
SELECT A FROM Trained GROUP BY A HAVING COUNT(A)
I'm not sure if this is correct, but it should be similar.
answered Oct 23 '16 at 16:56
user1766555user1766555
3092618
$endgroup$
add a comment |
$begingroup$
You use GROUP and HAVING. I don't know how your class does notation, but in mine we do something like this:
SELECT A FROM Trained GROUP BY A HAVING COUNT(A)
I'm not sure if this is correct, but it should be similar.
answered Oct 23 '16 at 16:56
user1766555user1766555
3092618
$endgroup$
You use GROUP and HAVING. I don't know how your class does notation, but in mine we do something like this:
SELECT A FROM Trained GROUP BY A HAVING COUNT(A)
I'm not sure if this is correct, but it should be similar.
answered Oct 23 '16 at 16:56
user1766555user1766555
3092618
edited Oct 23 '16 at 17:01
answered Oct 23 '16 at 16:56
user1766555user1766555
3092618
answered Oct 23 '16 at 16:56
user1766555user1766555
3092618
answered Oct 23 '16 at 16:56
user1766555user1766555
3092618
3092618
add a comment |
add a comment |
$begingroup$
Yes, it is possible to express it in relational algebra (RA).
The following line groups column A by COUNT(A). And plots COUNT(A) as 'frequencyOf_A'.
γ A; COUNT(A)→frequencyOf_A (Trained)
Resulting in this:
Trained.A frequencyOf_A
John 3
Willson 1
Kenny 1
Ho 1
I used this RA engine. And uploaded your relation via github's gist. Thanks. (On the side "relation algebra" is mathematics, while "relational algebra" is considered computer science I think.)
answered Oct 17 '17 at 23:44
Petr KosvanecPetr Kosvanec
11
$endgroup$
add a comment |
$begingroup$
Yes, it is possible to express it in relational algebra (RA).
The following line groups column A by COUNT(A). And plots COUNT(A) as 'frequencyOf_A'.
γ A; COUNT(A)→frequencyOf_A (Trained)
Resulting in this:
Trained.A frequencyOf_A
John 3
Willson 1
Kenny 1
Ho 1
I used this RA engine. And uploaded your relation via github's gist. Thanks. (On the side "relation algebra" is mathematics, while "relational algebra" is considered computer science I think.)
answered Oct 17 '17 at 23:44
Petr KosvanecPetr Kosvanec
11
$endgroup$
add a comment |
$begingroup$
Yes, it is possible to express it in relational algebra (RA).
The following line groups column A by COUNT(A). And plots COUNT(A) as 'frequencyOf_A'.
γ A; COUNT(A)→frequencyOf_A (Trained)
Resulting in this:
Trained.A frequencyOf_A
John 3
Willson 1
Kenny 1
Ho 1
I used this RA engine. And uploaded your relation via github's gist. Thanks. (On the side "relation algebra" is mathematics, while "relational algebra" is considered computer science I think.)
answered Oct 17 '17 at 23:44
Petr KosvanecPetr Kosvanec
11
$endgroup$
Yes, it is possible to express it in relational algebra (RA).
The following line groups column A by COUNT(A). And plots COUNT(A) as 'frequencyOf_A'.
γ A; COUNT(A)→frequencyOf_A (Trained)
Resulting in this:
Trained.A frequencyOf_A
John 3
Willson 1
Kenny 1
Ho 1
I used this RA engine. And uploaded your relation via github's gist. Thanks. (On the side "relation algebra" is mathematics, while "relational algebra" is considered computer science I think.)
answered Oct 17 '17 at 23:44
Petr KosvanecPetr Kosvanec
11
edited Oct 18 '17 at 0:14
answered Oct 17 '17 at 23:44
Petr KosvanecPetr Kosvanec
11
answered Oct 17 '17 at 23:44
Petr KosvanecPetr Kosvanec
11
answered Oct 17 '17 at 23:44
Petr KosvanecPetr Kosvanec
11
11
add a comment |
add a comment |
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