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Identifying candidate keys and primary keys
comp.databases.theory comp.databases.theory
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#41
 
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Re: Identifying candidate keys and primary keys -
04-13-2008
, 08:50 PM
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On Apr 13, 7:05 am, "Brian Selzer" <br... (AT) selzer-software (DOT) com> wrote: noagbodjivic... (AT) gmail (DOT) com> wrote in message news:fc37fe0e-476b-4a0b-8396-ab81c9a5f4a1 (AT) u69g2000hse (DOT) googlegroups.com... Hello guys, this one is for one of my assignments. I want explanations and hints only. I'm still confused with the concepts of candidate keys and primary key. We have a patient medication form from an hospital with these: Heading: Patient number, Full name, Bed number, Ward number, Ward name. Then a table with this columns: drug number, name, description, dosage, method of admin, units per day, start date, finish date. I have to find all the candidate keys and primary keys. I think candidate keys are the minimal superkeys. I have found {Patient number, Ward number, Ward name}. I have excluded {Patient number, Ward number, Ward name, Full name} and {Patient number, Ward number, Ward name, Full name, Bed number} which are also superkeys but contain more attributes. Can a patient be in more than one ward (at the same time)? This means that I have found only one candidate key, and this is also the primary key I have found (a composite). Since the question was "identify all the candidate keys" I thought maybe I dont really understand the concepts... http://en.wikipedia.org/wiki/Candidate_key thanks for any help. Brian, I don't really know... I have been looking at how hospitals work here in US. From what I have learned online, I don't think it's possible to have a patient in multiple ward at the same time (and I can't confirm). Also from what I have learned it seems like the ward names are unique in hospital. It probably means that a ward number assigned to a name is also unique. So that when we take a name, we have the number. But I can't confirm that either, I have found all this by searching online... |
identify the candidate keys. If you don't know enough about the subject
matter (or weren't provided with that information as part of the
assignment), then you might as well join Bluto.
#42
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On Apr 13, 7:05 am, "Brian Selzer" <br... (AT) selzer-software (DOT) com> wrote: noagbodjivic... (AT) gmail (DOT) com> wrote in message news:fc37fe0e-476b-4a0b-8396-ab81c9a5f4a1 (AT) u69g2000hse (DOT) googlegroups.com... Hello guys, this one is for one of my assignments. I want explanations and hints only. I'm still confused with the concepts of candidate keys and primary key. We have a patient medication form from an hospital with these: Heading: Patient number, Full name, Bed number, Ward number, Ward name. Then a table with this columns: drug number, name, description, dosage, method of admin, units per day, start date, finish date. I have to find all the candidate keys and primary keys. I think candidate keys are the minimal superkeys. I have found {Patient number, Ward number, Ward name}. I have excluded {Patient number, Ward number, Ward name, Full name} and {Patient number, Ward number, Ward name, Full name, Bed number} which are also superkeys but contain more attributes. Can a patient be in more than one ward (at the same time)? This means that I have found only one candidate key, and this is also the primary key I have found (a composite). Since the question was "identify all the candidate keys" I thought maybe I dont really understand the concepts... http://en.wikipedia.org/wiki/Candidate_key thanks for any help. Brian, I don't really know... I have been looking at how hospitals work here in US. From what I have learned online, I don't think it's possible to have a patient in multiple ward at the same time (and I can't confirm). Also from what I have learned it seems like the ward names are unique in hospital. It probably means that a ward number assigned to a name is also unique. So that when we take a name, we have the number. But I can't confirm that either, I have found all this by searching online... |
identify the candidate keys. If you don't know enough about the subject
matter (or weren't provided with that information as part of the
assignment), then you might as well join Bluto.
#43
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On Apr 13, 7:05 am, "Brian Selzer" <br... (AT) selzer-software (DOT) com> wrote: noagbodjivic... (AT) gmail (DOT) com> wrote in message news:fc37fe0e-476b-4a0b-8396-ab81c9a5f4a1 (AT) u69g2000hse (DOT) googlegroups.com... Hello guys, this one is for one of my assignments. I want explanations and hints only. I'm still confused with the concepts of candidate keys and primary key. We have a patient medication form from an hospital with these: Heading: Patient number, Full name, Bed number, Ward number, Ward name. Then a table with this columns: drug number, name, description, dosage, method of admin, units per day, start date, finish date. I have to find all the candidate keys and primary keys. I think candidate keys are the minimal superkeys. I have found {Patient number, Ward number, Ward name}. I have excluded {Patient number, Ward number, Ward name, Full name} and {Patient number, Ward number, Ward name, Full name, Bed number} which are also superkeys but contain more attributes. Can a patient be in more than one ward (at the same time)? This means that I have found only one candidate key, and this is also the primary key I have found (a composite). Since the question was "identify all the candidate keys" I thought maybe I dont really understand the concepts... http://en.wikipedia.org/wiki/Candidate_key thanks for any help. Brian, I don't really know... I have been looking at how hospitals work here in US. From what I have learned online, I don't think it's possible to have a patient in multiple ward at the same time (and I can't confirm). Also from what I have learned it seems like the ward names are unique in hospital. It probably means that a ward number assigned to a name is also unique. So that when we take a name, we have the number. But I can't confirm that either, I have found all this by searching online... |
identify the candidate keys. If you don't know enough about the subject
matter (or weren't provided with that information as part of the
assignment), then you might as well join Bluto.
#44
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On Apr 13, 7:05 am, "Brian Selzer" <br... (AT) selzer-software (DOT) com> wrote: noagbodjivic... (AT) gmail (DOT) com> wrote in message news:fc37fe0e-476b-4a0b-8396-ab81c9a5f4a1 (AT) u69g2000hse (DOT) googlegroups.com... Hello guys, this one is for one of my assignments. I want explanations and hints only. I'm still confused with the concepts of candidate keys and primary key. We have a patient medication form from an hospital with these: Heading: Patient number, Full name, Bed number, Ward number, Ward name. Then a table with this columns: drug number, name, description, dosage, method of admin, units per day, start date, finish date. I have to find all the candidate keys and primary keys. I think candidate keys are the minimal superkeys. I have found {Patient number, Ward number, Ward name}. I have excluded {Patient number, Ward number, Ward name, Full name} and {Patient number, Ward number, Ward name, Full name, Bed number} which are also superkeys but contain more attributes. Can a patient be in more than one ward (at the same time)? This means that I have found only one candidate key, and this is also the primary key I have found (a composite). Since the question was "identify all the candidate keys" I thought maybe I dont really understand the concepts... http://en.wikipedia.org/wiki/Candidate_key thanks for any help. Brian, I don't really know... I have been looking at how hospitals work here in US. From what I have learned online, I don't think it's possible to have a patient in multiple ward at the same time (and I can't confirm). Also from what I have learned it seems like the ward names are unique in hospital. It probably means that a ward number assigned to a name is also unique. So that when we take a name, we have the number. But I can't confirm that either, I have found all this by searching online... |
identify the candidate keys. If you don't know enough about the subject
matter (or weren't provided with that information as part of the
assignment), then you might as well join Bluto.
#45
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On Apr 13, 7:05 am, "Brian Selzer" <br... (AT) selzer-software (DOT) com> wrote: noagbodjivic... (AT) gmail (DOT) com> wrote in message news:fc37fe0e-476b-4a0b-8396-ab81c9a5f4a1 (AT) u69g2000hse (DOT) googlegroups.com... Hello guys, this one is for one of my assignments. I want explanations and hints only. I'm still confused with the concepts of candidate keys and primary key. We have a patient medication form from an hospital with these: Heading: Patient number, Full name, Bed number, Ward number, Ward name. Then a table with this columns: drug number, name, description, dosage, method of admin, units per day, start date, finish date. I have to find all the candidate keys and primary keys. I think candidate keys are the minimal superkeys. I have found {Patient number, Ward number, Ward name}. I have excluded {Patient number, Ward number, Ward name, Full name} and {Patient number, Ward number, Ward name, Full name, Bed number} which are also superkeys but contain more attributes. Can a patient be in more than one ward (at the same time)? This means that I have found only one candidate key, and this is also the primary key I have found (a composite). Since the question was "identify all the candidate keys" I thought maybe I dont really understand the concepts... http://en.wikipedia.org/wiki/Candidate_key thanks for any help. Brian, I don't really know... I have been looking at how hospitals work here in US. From what I have learned online, I don't think it's possible to have a patient in multiple ward at the same time (and I can't confirm). Also from what I have learned it seems like the ward names are unique in hospital. It probably means that a ward number assigned to a name is also unique. So that when we take a name, we have the number. But I can't confirm that either, I have found all this by searching online... |
identify the candidate keys. If you don't know enough about the subject
matter (or weren't provided with that information as part of the
assignment), then you might as well join Bluto.
#46
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On Apr 13, 7:05 am, "Brian Selzer" <br... (AT) selzer-software (DOT) com> wrote: noagbodjivic... (AT) gmail (DOT) com> wrote in message news:fc37fe0e-476b-4a0b-8396-ab81c9a5f4a1 (AT) u69g2000hse (DOT) googlegroups.com... Hello guys, this one is for one of my assignments. I want explanations and hints only. I'm still confused with the concepts of candidate keys and primary key. We have a patient medication form from an hospital with these: Heading: Patient number, Full name, Bed number, Ward number, Ward name. Then a table with this columns: drug number, name, description, dosage, method of admin, units per day, start date, finish date. I have to find all the candidate keys and primary keys. I think candidate keys are the minimal superkeys. I have found {Patient number, Ward number, Ward name}. I have excluded {Patient number, Ward number, Ward name, Full name} and {Patient number, Ward number, Ward name, Full name, Bed number} which are also superkeys but contain more attributes. Can a patient be in more than one ward (at the same time)? This means that I have found only one candidate key, and this is also the primary key I have found (a composite). Since the question was "identify all the candidate keys" I thought maybe I dont really understand the concepts... http://en.wikipedia.org/wiki/Candidate_key thanks for any help. Brian, I don't really know... I have been looking at how hospitals work here in US. From what I have learned online, I don't think it's possible to have a patient in multiple ward at the same time (and I can't confirm). Also from what I have learned it seems like the ward names are unique in hospital. It probably means that a ward number assigned to a name is also unique. So that when we take a name, we have the number. But I can't confirm that either, I have found all this by searching online... |
identify the candidate keys. If you don't know enough about the subject
matter (or weren't provided with that information as part of the
assignment), then you might as well join Bluto.
#47
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We have a patient medication form from an hospital with these: Heading: Patient number, Full name, Bed number, Ward number, Ward name. Then a table with this columns: drug number, name, description, dosage, method of admin, units per day, start date, finish date. I have to find all the candidate keys and primary keys. |
then the keys. As the requirements were quite vague, my guess (without
prejudice) here. Play with it a bit and see if it leads to an answer.
Patients
-----------
PatientNumber - Primary key
FirstName \ bad candidate key if two persons have the same name
LastName /
Wards
---------
WardNumber - Primary key
WardName - candidate key (?) No idea if the name is unique, but it is
likely.
PatientLocations
-----------------------
PatientNumber --- \
WardNumber --- composite primary key
BedNumber --- /
I could imagine a patient can change the ward during its stay in
hospital, so might add StartDate, EndDate pair, but that was not
mentioned in the specification.
Drugs
-----------
DrugNumber - Primary key
DrugName - candidate key (?) Is a drug name always unique?
DrugDescription
Treatments
----------------
PatientNumber \
DrugNumber --- composite primary key
StartDate /
FinishDate /
Dosage
MethodOfAdmin
UnitsPerDay
I would assume that the same drug can be given through out several
periods of time, therefore I put the dates into the PK.
Brgds
Philipp Post
#48
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We have a patient medication form from an hospital with these: Heading: Patient number, Full name, Bed number, Ward number, Ward name. Then a table with this columns: drug number, name, description, dosage, method of admin, units per day, start date, finish date. I have to find all the candidate keys and primary keys. |
then the keys. As the requirements were quite vague, my guess (without
prejudice) here. Play with it a bit and see if it leads to an answer.
Patients
-----------
PatientNumber - Primary key
FirstName \ bad candidate key if two persons have the same name
LastName /
Wards
---------
WardNumber - Primary key
WardName - candidate key (?) No idea if the name is unique, but it is
likely.
PatientLocations
-----------------------
PatientNumber --- \
WardNumber --- composite primary key
BedNumber --- /
I could imagine a patient can change the ward during its stay in
hospital, so might add StartDate, EndDate pair, but that was not
mentioned in the specification.
Drugs
-----------
DrugNumber - Primary key
DrugName - candidate key (?) Is a drug name always unique?
DrugDescription
Treatments
----------------
PatientNumber \
DrugNumber --- composite primary key
StartDate /
FinishDate /
Dosage
MethodOfAdmin
UnitsPerDay
I would assume that the same drug can be given through out several
periods of time, therefore I put the dates into the PK.
Brgds
Philipp Post
#49
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We have a patient medication form from an hospital with these: Heading: Patient number, Full name, Bed number, Ward number, Ward name. Then a table with this columns: drug number, name, description, dosage, method of admin, units per day, start date, finish date. I have to find all the candidate keys and primary keys. |
then the keys. As the requirements were quite vague, my guess (without
prejudice) here. Play with it a bit and see if it leads to an answer.
Patients
-----------
PatientNumber - Primary key
FirstName \ bad candidate key if two persons have the same name
LastName /
Wards
---------
WardNumber - Primary key
WardName - candidate key (?) No idea if the name is unique, but it is
likely.
PatientLocations
-----------------------
PatientNumber --- \
WardNumber --- composite primary key
BedNumber --- /
I could imagine a patient can change the ward during its stay in
hospital, so might add StartDate, EndDate pair, but that was not
mentioned in the specification.
Drugs
-----------
DrugNumber - Primary key
DrugName - candidate key (?) Is a drug name always unique?
DrugDescription
Treatments
----------------
PatientNumber \
DrugNumber --- composite primary key
StartDate /
FinishDate /
Dosage
MethodOfAdmin
UnitsPerDay
I would assume that the same drug can be given through out several
periods of time, therefore I put the dates into the PK.
Brgds
Philipp Post
#50
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We have a patient medication form from an hospital with these: Heading: Patient number, Full name, Bed number, Ward number, Ward name. Then a table with this columns: drug number, name, description, dosage, method of admin, units per day, start date, finish date. I have to find all the candidate keys and primary keys. |
then the keys. As the requirements were quite vague, my guess (without
prejudice) here. Play with it a bit and see if it leads to an answer.
Patients
-----------
PatientNumber - Primary key
FirstName \ bad candidate key if two persons have the same name
LastName /
Wards
---------
WardNumber - Primary key
WardName - candidate key (?) No idea if the name is unique, but it is
likely.
PatientLocations
-----------------------
PatientNumber --- \
WardNumber --- composite primary key
BedNumber --- /
I could imagine a patient can change the ward during its stay in
hospital, so might add StartDate, EndDate pair, but that was not
mentioned in the specification.
Drugs
-----------
DrugNumber - Primary key
DrugName - candidate key (?) Is a drug name always unique?
DrugDescription
Treatments
----------------
PatientNumber \
DrugNumber --- composite primary key
StartDate /
FinishDate /
Dosage
MethodOfAdmin
UnitsPerDay
I would assume that the same drug can be given through out several
periods of time, therefore I put the dates into the PK.
Brgds
Philipp Post
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