Data Repeated

[farhaaad]

Dears,

I have many feilds in my tables that are left blank for some records,
If I make a sub table for it and and change those feilds to a lookup
feilds so only those options are chosen which fit to the table, some
information will be repeated for all records.
Example: I have table for the cities in the country
tblCity(cityID( pk), City(text), river(yes/no), airport(yes/no),
tower(yes/no)
Here, mayb a city has all the three (river, airport, tower) and
another city wont have any of them.
So, I made a sub table with a lookup feild and the three choices in
the feild. here if two cities have airports, airport is mentioned
twice in the same subtable.
I hope you got me,
I appreciate your help,
Farhaad

[Allen Browne]

So the junction table will have fields for CityID and Feature, and you will
have records like this:
CityID Feature
==== ======
2 Airport
2 River
3 Airport
3 Tower

What's wrong with that?

--
Allen Browne - Microsoft MVP. Perth, Western Australia
Tips for Access users - http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

<fa******@gmail .comwrote in message
news:11******** **************@ o5g2000hsb.goog legroups.com...

Dears,

I have many feilds in my tables that are left blank for some records,
If I make a sub table for it and and change those feilds to a lookup
feilds so only those options are chosen which fit to the table, some
information will be repeated for all records.

Example: I have table for the cities in the country
tblCity(cityID( pk), City(text), river(yes/no), airport(yes/no),
tower(yes/no)
Here, mayb a city has all the three (river, airport, tower) and
another city wont have any of them.
So, I made a sub table with a lookup feild and the three choices in
the feild. here if two cities have airports, airport is mentioned
twice in the same subtable.

I hope you got me,
I appreciate your help,

Farhaad

[farhaaad]

On Apr 23, 9:47 am, "Allen Browne" <AllenBro...@Se eSig.Invalidwro te:

So the junction table will have fields for CityID and Feature, and you will
have records like this:
CityID Feature
==== ======
2 Airport
2 River
3 Airport
3 Tower

What's wrong with that?

--
Allen Browne - Microsoft MVP. Perth, Western Australia
Tips for Access users -http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

<farha...@gmail .comwrote in message

news:11******** **************@ o5g2000hsb.goog legroups.com...

Dears,

I have many feilds in my tables that are left blank for some records,
If I make a sub table for it and and change those feilds to a lookup
feilds so only those options are chosen which fit to the table, some
information will be repeated for all records.

Example: I have table for the cities in the country
tblCity(cityID( pk), City(text), river(yes/no), airport(yes/no),
tower(yes/no)
Here, mayb a city has all the three (river, airport, tower) and
another city wont have any of them.
So, I made a sub table with a lookup feild and the three choices in
the feild. here if two cities have airports, airport is mentioned
twice in the same subtable.

I hope you got me,
I appreciate your help,

Farhaad- Hide quoted text -

- Show quoted text -

Sir,

I just want to know if we can avoid the repition of data in the sub
table.

Thanks alot,

[Allen Browne]

No. That's the right structure.

Ultimately you have 3 tables:
Table 1 = a list of cities;
Table 2 = a list of features;
Table 3 = the junction table between the other two (matching cities and
features.)

That is the standard way to resolve a many-to-many relation into a pair of
one-to-many relations.

--
Allen Browne - Microsoft MVP. Perth, Western Australia
Tips for Access users - http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

<fa******@gmail .comwrote in message
news:11******** **************@ o5g2000hsb.goog legroups.com...

On Apr 23, 9:47 am, "Allen Browne" <AllenBro...@Se eSig.Invalidwro te:

>So the junction table will have fields for CityID and Feature, and you
will
have records like this:
CityID Feature
==== ======
2 Airport
2 River
3 Airport
3 Tower

What's wrong with that?

--
Allen Browne - Microsoft MVP. Perth, Western Australia
Tips for Access users -http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

<farha...@gmai l.comwrote in message

news:11******* *************** @o5g2000hsb.goo glegroups.com.. .

Dears,

I have many feilds in my tables that are left blank for some records,
If I make a sub table for it and and change those feilds to a lookup
feilds so only those options are chosen which fit to the table, some
information will be repeated for all records.

Example: I have table for the cities in the country
tblCity(cityID( pk), City(text), river(yes/no), airport(yes/no),
tower(yes/no)
Here, mayb a city has all the three (river, airport, tower) and
another city wont have any of them.
So, I made a sub table with a lookup feild and the three choices in
the feild. here if two cities have airports, airport is mentioned
twice in the same subtable.

I hope you got me,
I appreciate your help,

Farhaad- Hide quoted text -

- Show quoted text -

Sir,

I just want to know if we can avoid the repition of data in the sub
table.

Thanks alot,

[farhaaad]

On Apr 23, 4:26 pm, "Allen Browne" <AllenBro...@Se eSig.Invalidwro te:

No. That's the right structure.

Ultimately you have 3 tables:
Table 1 = a list of cities;
Table 2 = a list of features;
Table 3 = the junction table between the other two (matching cities and
features.)

That is the standard way to resolve a many-to-many relation into a pair of
one-to-many relations.

--
Allen Browne - Microsoft MVP. Perth, Western Australia
Tips for Access users -http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

<farha...@gmail .comwrote in message

news:11******** **************@ o5g2000hsb.goog legroups.com...

On Apr 23, 9:47 am, "Allen Browne" <AllenBro...@Se eSig.Invalidwro te:

So the junction table will have fields for CityID and Feature, and you
will
have records like this:
CityID Feature
==== ======
2 Airport
2 River
3 Airport
3 Tower

What's wrong with that?

--
Allen Browne - Microsoft MVP. Perth, Western Australia
Tips for Access users -http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

<farha...@gmail .comwrote in message

>news:11******* *************** @o5g2000hsb.goo glegroups.com.. .

Dears,

I have many feilds in my tables that are left blank for some records,
If I make a sub table for it and and change those feilds to a lookup
feilds so only those options are chosen which fit to the table, some
information will be repeated for all records.

Example: I have table for the cities in the country
tblCity(cityID( pk), City(text), river(yes/no), airport(yes/no),
tower(yes/no)
Here, mayb a city has all the three (river, airport, tower) and
another city wont have any of them.
So, I made a sub table with a lookup feild and the three choices in
the feild. here if two cities have airports, airport is mentioned
twice in the same subtable.

I hope you got me,
I appreciate your help,

Farhaad- Hide quoted text -

- Show quoted text -

Sir,

I just want to know if we can avoid the repition of data in the sub
table.

Thanks alot,- Hide quoted text -

- Show quoted text -

Thanks alot for the help and Sir!

Can a primary key have many foreing keys? and can these foreign tables
have different structures depeding on primary keys?
for example, tblCity(CityID, City)1to1 tbl(CityID (fk),
Features(pk)1to many tblTrade(Featur es(fk),TradCent ers(integer)),
tblAirport(feat ures(fk),
Area(integer),R unways(integer) ,Terminals(inte ger))
tblhospital(fea tures(fk),Locat ion, Capacity(ingege r),
Doctors(Integer ), Nurses(Integer) ).

I hope you got some Idea from the above example, Suppose we have three
features (Airport,TradeC enter and Hospital) for each city and each
feature has its own attribute so I made seperate tables for each.

I again thank you very much for the help and I hope you help me with
the above structure if it is ok or should I change it?

I appreciate your extraordinary intelligence in databases and helping
others,

[Allen Browne]

No. That's not right.

You need a Feature table, with a field like this:
FeatureID Text primary key
Then you enter *records* such as:
Airport
Tower
River

The junction table then has fields like this:
CityID relates to the primary key of the City table
FeatureID relates to the primary key of the Feature table.
So the records in this table look like the example in the previous reply.

--
Allen Browne - Microsoft MVP. Perth, Western Australia
Tips for Access users - http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

<fa******@gmail .comwrote in message
news:11******** **************@ o5g2000hsb.goog legroups.com...

On Apr 23, 4:26 pm, "Allen Browne" <AllenBro...@Se eSig.Invalidwro te:

>No. That's the right structure.

Ultimately you have 3 tables:
Table 1 = a list of cities;
Table 2 = a list of features;
Table 3 = the junction table between the other two (matching cities and
features.)

That is the standard way to resolve a many-to-many relation into a pair
of
one-to-many relations.

--
Allen Browne - Microsoft MVP. Perth, Western Australia
Tips for Access users -http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

<farha...@gmai l.comwrote in message

news:11******* *************** @o5g2000hsb.goo glegroups.com.. .

On Apr 23, 9:47 am, "Allen Browne" <AllenBro...@Se eSig.Invalidwro te:
So the junction table will have fields for CityID and Feature, and you
will
have records like this:
CityID Feature
==== ======
2 Airport
2 River
3 Airport
3 Tower

>What's wrong with that?

><farha...@gmai l.comwrote in message

>>news:11****** *************** *@o5g2000hsb.go oglegroups.com. ..

Dears,

I have many feilds in my tables that are left blank for some
records,
If I make a sub table for it and and change those feilds to a lookup
feilds so only those options are chosen which fit to the table, some
information will be repeated for all records.

Example: I have table for the cities in the country
tblCity(cityID( pk), City(text), river(yes/no), airport(yes/no),
tower(yes/no)
Here, mayb a city has all the three (river, airport, tower) and
another city wont have any of them.
So, I made a sub table with a lookup feild and the three choices in
the feild. here if two cities have airports, airport is mentioned
twice in the same subtable.

I hope you got me,
I appreciate your help,

Farhaad- Hide quoted text -

>- Show quoted text -

Sir,

I just want to know if we can avoid the repition of data in the sub
table.

Thanks alot,- Hide quoted text -

- Show quoted text -

Thanks alot for the help and Sir!

Can a primary key have many foreing keys? and can these foreign tables
have different structures depeding on primary keys?
for example, tblCity(CityID, City)1to1 tbl(CityID (fk),
Features(pk)1to many tblTrade(Featur es(fk),TradCent ers(integer)),
tblAirport(feat ures(fk),
Area(integer),R unways(integer) ,Terminals(inte ger))
tblhospital(fea tures(fk),Locat ion, Capacity(ingege r),
Doctors(Integer ), Nurses(Integer) ).

I hope you got some Idea from the above example, Suppose we have three
features (Airport,TradeC enter and Hospital) for each city and each
feature has its own attribute so I made seperate tables for each.

I again thank you very much for the help and I hope you help me with
the above structure if it is ok or should I change it?

I appreciate your extraordinary intelligence in databases and helping
others,

[farhaaad]

On Apr 24, 8:42 am, "Allen Browne" <AllenBro...@Se eSig.Invalidwro te:

No. That's not right.

You need a Feature table, with a field like this:
FeatureID Text primary key
Then you enter *records* such as:
Airport
Tower
River

The junction table then has fields like this:
CityID relates to the primary key of the City table
FeatureID relates to the primary key of the Feature table.
So the records in this table look like the example in the previous reply.

--
Allen Browne - Microsoft MVP. Perth, Western Australia
Tips for Access users -http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

<farha...@gmail .comwrote in message

news:11******** **************@ o5g2000hsb.goog legroups.com...

On Apr 23, 4:26 pm, "Allen Browne" <AllenBro...@Se eSig.Invalidwro te:

No. That's the right structure.

Ultimately you have 3 tables:
Table 1 = a list of cities;
Table 2 = a list of features;
Table 3 = the junction table between the other two (matching cities and
features.)

That is the standard way to resolve a many-to-many relation into a pair
of
one-to-many relations.

--
Allen Browne - Microsoft MVP. Perth, Western Australia
Tips for Access users -http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

<farha...@gmail .comwrote in message

>news:11******* *************** @o5g2000hsb.goo glegroups.com.. .

On Apr 23, 9:47 am, "Allen Browne" <AllenBro...@Se eSig.Invalidwro te:
So the junction table will have fields for CityID and Feature, and you
will
have records like this:
CityID Feature
==== ======
2 Airport
2 River
3 Airport
3 Tower

What's wrong with that?

<farha...@gmail .comwrote in message

>news:11******* *************** @o5g2000hsb.goo glegroups.com.. .

Dears,

I have many feilds in my tables that are left blank for some
records,
If I make a sub table for it and and change those feilds to a lookup
feilds so only those options are chosen which fit to the table, some
information will be repeated for all records.

Example: I have table for the cities in the country
tblCity(cityID( pk), City(text), river(yes/no), airport(yes/no),
tower(yes/no)
Here, mayb a city has all the three (river, airport, tower) and
another city wont have any of them.
So, I made a sub table with a lookup feild and the three choices in
the feild. here if two cities have airports, airport is mentioned
twice in the same subtable.

I hope you got me,
I appreciate your help,

Farhaad- Hide quoted text -

- Show quoted text -

Sir,

I just want to know if we can avoid the repition of data in the sub
table.

Thanks alot,- Hide quoted text -

- Show quoted text -

Thanks alot for the help and Sir!

Can a primary key have many foreing keys? and can these foreign tables
have different structures depeding on primary keys?
for example, tblCity(CityID, City)1to1 tbl(CityID (fk),
Features(pk)1to many tblTrade(Featur es(fk),TradCent ers(integer)),
tblAirport(feat ures(fk),
Area(integer),R unways(integer) ,Terminals(inte ger))
tblhospital(fea tures(fk),Locat ion, Capacity(ingege r),
Doctors(Integer ), Nurses(Integer) ).

I hope you got some Idea from the above example, Suppose we have three
features (Airport,TradeC enter and Hospital) for each city and each
feature has its own attribute so I made seperate tables for each.

I again thank you very much for the help and I hope you help me with
the above structure if it is ok or should I change it?

I appreciate your extraordinary intelligence in databases and helping
others,- Hide quoted text -

- Show quoted text -

Thank you sir,

What I mean here is that each primary key in features table relates to
a different table. For example (airport,city,t ower) have their own
tables and foreign keys for the feature table.

is that ok?

I thank you very much

[Allen Browne]

No. that is not okay.

--
Allen Browne - Microsoft MVP. Perth, Western Australia
Tips for Access users - http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.
<fa******@gmail .comwrote in message
news:11******** **************@ r30g2000prh.goo glegroups.com.. .

On Apr 24, 8:42 am, "Allen Browne" <AllenBro...@Se eSig.Invalidwro te:

>No. That's not right.

You need a Feature table, with a field like this:
FeatureID Text primary key
Then you enter *records* such as:
Airport
Tower
River

The junction table then has fields like this:
CityID relates to the primary key of the City table
FeatureID relates to the primary key of the Feature table.
So the records in this table look like the example in the previous reply.

--
Allen Browne - Microsoft MVP. Perth, Western Australia
Tips for Access users -http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

<farha...@gmai l.comwrote in message

news:11******* *************** @o5g2000hsb.goo glegroups.com.. .

On Apr 23, 4:26 pm, "Allen Browne" <AllenBro...@Se eSig.Invalidwro te:
No. That's the right structure.

>Ultimately you have 3 tables:
Table 1 = a list of cities;
Table 2 = a list of features;
Table 3 = the junction table between the other two (matching cities
and
features.)

>That is the standard way to resolve a many-to-many relation into a
pair
of
one-to-many relations.

>--
Allen Browne - Microsoft MVP. Perth, Western Australia
Tips for Access users -http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

><farha...@gmai l.comwrote in message

>>news:11****** *************** *@o5g2000hsb.go oglegroups.com. ..

On Apr 23, 9:47 am, "Allen Browne" <AllenBro...@Se eSig.Invalid>
wrote:
So the junction table will have fields for CityID and Feature, and
you
will
have records like this:
CityID Feature
==== ======
2 Airport
2 River
3 Airport
3 Tower

>What's wrong with that?

><farha...@gmai l.comwrote in message

>>news:11****** *************** *@o5g2000hsb.go oglegroups.com. ..

Dears,

I have many feilds in my tables that are left blank for some
records,
If I make a sub table for it and and change those feilds to a
lookup
feilds so only those options are chosen which fit to the table,
some
information will be repeated for all records.

Example: I have table for the cities in the country
tblCity(cityID( pk), City(text), river(yes/no), airport(yes/no),
tower(yes/no)
Here, mayb a city has all the three (river, airport, tower) and
another city wont have any of them.
So, I made a sub table with a lookup feild and the three choices
in
the feild. here if two cities have airports, airport is mentioned
twice in the same subtable.

I hope you got me,
I appreciate your help,

Farhaad- Hide quoted text -

>- Show quoted text -

Sir,

I just want to know if we can avoid the repition of data in the sub
table.

Thanks alot,- Hide quoted text -

>- Show quoted text -

Thanks alot for the help and Sir!

Can a primary key have many foreing keys? and can these foreign tables
have different structures depeding on primary keys?
for example, tblCity(CityID, City)1to1 tbl(CityID (fk),
Features(pk)1to many tblTrade(Featur es(fk),TradCent ers(integer)),
tblAirport(feat ures(fk),
Area(integer),R unways(integer) ,Terminals(inte ger))
tblhospital(fea tures(fk),Locat ion, Capacity(ingege r),
Doctors(Integer ), Nurses(Integer) ).

I hope you got some Idea from the above example, Suppose we have three
features (Airport,TradeC enter and Hospital) for each city and each
feature has its own attribute so I made seperate tables for each.

I again thank you very much for the help and I hope you help me with
the above structure if it is ok or should I change it?

I appreciate your extraordinary intelligence in databases and helping
others,- Hide quoted text -

- Show quoted text -

Thank you sir,

What I mean here is that each primary key in features table relates to
a different table. For example (airport,city,t ower) have their own
tables and foreign keys for the feature table.

is that ok?

I thank you very much

[farhaaad]

On Apr 24, 10:23 am, "Allen Browne" <AllenBro...@Se eSig.Invalid>
wrote:

No. that is not okay.

--
Allen Browne - Microsoft MVP. Perth, Western Australia
Tips for Access users -http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.<farha...@g mail.comwrote in message

news:11******** **************@ r30g2000prh.goo glegroups.com.. .

On Apr 24, 8:42 am, "Allen Browne" <AllenBro...@Se eSig.Invalidwro te:

No. That's not right.

You need a Feature table, with a field like this:
FeatureID Text primary key
Then you enter *records* such as:
Airport
Tower
River

The junction table then has fields like this:
CityID relates to the primary key of the City table
FeatureID relates to the primary key of the Feature table.
So the records in this table look like the example in the previous reply.

--
Allen Browne - Microsoft MVP. Perth, Western Australia
Tips for Access users -http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

<farha...@gmail .comwrote in message

>news:11******* *************** @o5g2000hsb.goo glegroups.com.. .

On Apr 23, 4:26 pm, "Allen Browne" <AllenBro...@Se eSig.Invalidwro te:
No. That's the right structure.

Ultimately you have 3 tables:
Table 1 = a list of cities;
Table 2 = a list of features;
Table 3 = the junction table between the other two (matching cities
and
features.)

That is the standard way to resolve a many-to-many relation into a
pair
of
one-to-many relations.

--
Allen Browne - Microsoft MVP. Perth, Western Australia
Tips for Access users -http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

<farha...@gmail .comwrote in message

>news:11******* *************** @o5g2000hsb.goo glegroups.com.. .

On Apr 23, 9:47 am, "Allen Browne" <AllenBro...@Se eSig.Invalid>
wrote:
So the junction table will have fields for CityID and Feature, and
you
will
have records like this:
CityID Feature
==== ======
2 Airport
2 River
3 Airport
3 Tower

What's wrong with that?

<farha...@gmail .comwrote in message

>news:11******* *************** @o5g2000hsb.goo glegroups.com.. .

Dears,

I have many feilds in my tables that are left blank for some
records,
If I make a sub table for it and and change those feilds to a
lookup
feilds so only those options are chosen which fit to the table,
some
information will be repeated for all records.

Example: I have table for the cities in the country
tblCity(cityID( pk), City(text), river(yes/no), airport(yes/no),
tower(yes/no)
Here, mayb a city has all the three (river, airport, tower) and
another city wont have any of them.
So, I made a sub table with a lookup feild and the three choices
in
the feild. here if two cities have airports, airport is mentioned
twice in the same subtable.

I hope you got me,
I appreciate your help,

Farhaad- Hide quoted text -

- Show quoted text -

Sir,

I just want to know if we can avoid the repition of data in the sub
table.

Thanks alot,- Hide quoted text -

- Show quoted text -

Thanks alot for the help and Sir!

Can a primary key have many foreing keys? and can these foreign tables
have different structures depeding on primary keys?
for example, tblCity(CityID, City)1to1 tbl(CityID (fk),
Features(pk)1to many tblTrade(Featur es(fk),TradCent ers(integer)),
tblAirport(feat ures(fk),
Area(integer),R unways(integer) ,Terminals(inte ger))
tblhospital(fea tures(fk),Locat ion, Capacity(ingege r),
Doctors(Integer ), Nurses(Integer) ).

I hope you got some Idea from the above example, Suppose we have three
features (Airport,TradeC enter and Hospital) for each city and each
feature has its own attribute so I made seperate tables for each.

I again thank you very much for the help and I hope you help me with
the above structure if it is ok or should I change it?

I appreciate your extraordinary intelligence in databases and helping
others,- Hide quoted text -

- Show quoted text -

Thank you sir,

What I mean here is that each primary key in features table relates to
a different table. For example (airport,city,t ower) have their own
tables and foreign keys for the feature table.

is that ok?

I thank you very much- Hide quoted text -

- Show quoted text -

Sir,
Each feature has its own attributes and I cannot bring all the
features in one table because some fields may be left blank for some
features. Pleas guide me what to do.

Thank alot

[Allen Browne]

Sorry: I'm out of suggestions.

You are closer to your data, and you know what you can and can't achieve. I
can't see it so all I can do is explain the normalized approach. If that
doesn't apply, you can take it from there, and it's time for me to move on
to answering other questions.

All the best

--
Allen Browne - Microsoft MVP. Perth, Western Australia
Tips for Access users - http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

<fa******@gmail .comwrote in message
news:11******** **************@ s33g2000prh.goo glegroups.com.. .

On Apr 24, 10:23 am, "Allen Browne" <AllenBro...@Se eSig.Invalid>
wrote:

>No. that is not okay.

news:11******* *************** @r30g2000prh.go oglegroups.com. ..

On Apr 24, 8:42 am, "Allen Browne" <AllenBro...@Se eSig.Invalidwro te:
No. That's not right.

>You need a Feature table, with a field like this:
FeatureID Text primary key
Then you enter *records* such as:
Airport
Tower
River

>The junction table then has fields like this:
CityID relates to the primary key of the City table
FeatureID relates to the primary key of the Feature table.
So the records in this table look like the example in the previous
reply.

>--
Allen Browne - Microsoft MVP. Perth, Western Australia
Tips for Access users -http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

><farha...@gmai l.comwrote in message

>>news:11****** *************** *@o5g2000hsb.go oglegroups.com. ..

On Apr 23, 4:26 pm, "Allen Browne" <AllenBro...@Se eSig.Invalid>
wrote:
No. That's the right structure.

>Ultimately you have 3 tables:
Table 1 = a list of cities;
Table 2 = a list of features;
Table 3 = the junction table between the other two (matching cities
and
features.)

>That is the standard way to resolve a many-to-many relation into a
pair
of
one-to-many relations.

>--
Allen Browne - Microsoft MVP. Perth, Western Australia
Tips for Access users -http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

><farha...@gmai l.comwrote in message

>>news:11****** *************** *@o5g2000hsb.go oglegroups.com. ..

On Apr 23, 9:47 am, "Allen Browne" <AllenBro...@Se eSig.Invalid>
wrote:
So the junction table will have fields for CityID and Feature,
and
you
will
have records like this:
CityID Feature
==== ======
2 Airport
2 River
3 Airport
3 Tower

>What's wrong with that?

><farha...@gmai l.comwrote in message

>>news:11****** *************** *@o5g2000hsb.go oglegroups.com. ..

Dears,

I have many feilds in my tables that are left blank for some
records,
If I make a sub table for it and and change those feilds to a
lookup
feilds so only those options are chosen which fit to the
table,
some
information will be repeated for all records.

Example: I have table for the cities in the country
tblCity(cityID( pk), City(text), river(yes/no),
airport(yes/no),
tower(yes/no)
Here, mayb a city has all the three (river, airport, tower)
and
another city wont have any of them.
So, I made a sub table with a lookup feild and the three
choices
in
the feild. here if two cities have airports, airport is
mentioned
twice in the same subtable.

I hope you got me,
I appreciate your help,

Farhaad- Hide quoted text -

>- Show quoted text -

Sir,

I just want to know if we can avoid the repition of data in the
sub
table.

Thanks alot,- Hide quoted text -

>- Show quoted text -

Thanks alot for the help and Sir!

Can a primary key have many foreing keys? and can these foreign
tables
have different structures depeding on primary keys?
for example, tblCity(CityID, City)1to1 tbl(CityID (fk),
Features(pk)1to many tblTrade(Featur es(fk),TradCent ers(integer)),
tblAirport(feat ures(fk),
Area(integer),R unways(integer) ,Terminals(inte ger))
tblhospital(fea tures(fk),Locat ion, Capacity(ingege r),
Doctors(Integer ), Nurses(Integer) ).

I hope you got some Idea from the above example, Suppose we have
three
features (Airport,TradeC enter and Hospital) for each city and each
feature has its own attribute so I made seperate tables for each.

I again thank you very much for the help and I hope you help me with
the above structure if it is ok or should I change it?

I appreciate your extraordinary intelligence in databases and
helping
others,- Hide quoted text -

>- Show quoted text -

Thank you sir,

What I mean here is that each primary key in features table relates to
a different table. For example (airport,city,t ower) have their own
tables and foreign keys for the feature table.

is that ok?

I thank you very much- Hide quoted text -

- Show quoted text -

Sir,
Each feature has its own attributes and I cannot bring all the
features in one table because some fields may be left blank for some
features. Pleas guide me what to do.

Thank alot