I have 3 tables: Message, Workgroup, and Hyperlink. Message has 1xM link
with Hyperlink and Workgroup has 1xM link with Hyperlink. Hyperlink has the
following fields:
IDhyperlink*
IDmessage
IDworkgroup
Name_Hyperlink
In most cases either IDmessage or IDworkgroup will have no value.
Is this a good approach or should I make 2 Hyperlink tables or...?
thanks,
john
18  2106 
"john" <jo**@test.coms chreef in bericht news:zP******** ************@ca sema.nl...
>I have 3 tables: Message, Workgroup, and Hyperlink. Message has 1xM link
with Hyperlink and Workgroup has 1xM link with Hyperlink. Hyperlink has the
following fields:
IDhyperlink*
IDmessage
IDworkgroup
Name_Hyperlink
In most cases either IDmessage or IDworkgroup will have no value.
Is this a good approach or should I make 2 Hyperlink tables or...?
thanks,
john
In most cases the way you have linked the tables is a model of a many to many relationship between Message and Workgroup.
You would need a value for both message and workgroup in table Hyperlink.
In your case I think you might as well skip the table Hyperlink.
Just store the Name_Hyperlink in the tables (or maybe make 2 hyperlink tables indeed)
Just guessing because I don't know your specs...
Arno R
"Arno R" <ar***********@ tiscali.nlschre ef in bericht
news:45******** **************@ text.nova.plane t.nl...
>In your case I think you might as well skip the table Hyperlink.
Just store the Name_Hyperlink in the tables (or maybe make 2 hyperlink
tables indeed)
Just guessing because I don't know your specs...
Thanks.
Just storing the Name_Hyperlink in the tables is not an option because one
Message can have more than one hyperlink. The same accounts for Workgroup. I
think I need to have 2 hyperlink tables, but I'd rather keep them in one
table. That's why I came up with the earlier mentioned solution.
john
"john" <jo**@test.coms chreef in bericht news:F5******** ************@ca sema.nl...
Thanks.
Just storing the Name_Hyperlink in the tables is not an option because one
Message can have more than one hyperlink. The same accounts for Workgroup. I
think I need to have 2 hyperlink tables, but I'd rather keep them in one
table. That's why I came up with the earlier mentioned solution.
john
After having 'consumed' this info IMO the best model is to use two hyperlink tables.
In general I think that allowing null in foreign keys is not a good idea. At least I try to avoid that.
So I do have problems with the 'no value' FK fields in your original solution...
Do a Google search on "allow null in FK" and you will find some interesting discussions and opinions about this issue.
Why the need to stick to one table ??
If needed you can use Union-query's to 'show' one 'table'.
Arno R
In article <zP************ ********@casema .nl>, jo**@test.com says...
I have 3 tables: Message, Workgroup, and Hyperlink. Message has 1xM link
with Hyperlink and Workgroup has 1xM link with Hyperlink. Hyperlink has the
following fields:
IDhyperlink*
IDmessage
IDworkgroup
Name_Hyperlink
In most cases either IDmessage or IDworkgroup will have no value.
Is this a good approach or should I make 2 Hyperlink tables or...?
thanks,
john
Perhaps this is a three-way relationship,
Workgroups is related to Hyperlinks 1 to Many,
Messages is related to Hyperlinks 1 to Many.
Workgroups
----------
workgroup_id PRIMARY KEY
and other columns
Messages
------------
message_id PRIMARY KEY
and other columns
Hyperlinks
-----------
hyperlink_id
workgroup_id
message_id
PRIMARY KEY (hyperlink_id,
workgroup_id,
message_id)
UNIQUE (workgoup_id,
message_id)
and other fields
I have seen this kind of relationship
discussed by others.
In article <MP************ ************@ne ws.psci.net>, gr******@psci.n et
says...
In article <zP************ ********@casema .nl>, jo**@test.com says...
I have 3 tables: Message, Workgroup, and Hyperlink. Message has 1xM link
with Hyperlink and Workgroup has 1xM link with Hyperlink. Hyperlink has the
following fields:
IDhyperlink*
IDmessage
IDworkgroup
Name_Hyperlink
In most cases either IDmessage or IDworkgroup will have no value.
Is this a good approach or should I make 2 Hyperlink tables or...?
thanks,
john
Perhaps this is a three-way relationship,
Workgroups is related to Hyperlinks 1 to Many,
Messages is related to Hyperlinks 1 to Many.
Workgroups
----------
workgroup_id PRIMARY KEY
and other columns
Messages
------------
message_id PRIMARY KEY
and other columns
Hyperlinks
-----------
hyperlink_id
workgroup_id
message_id
PRIMARY KEY (hyperlink_id,
workgroup_id,
message_id)
UNIQUE (workgoup_id,
message_id)
and other fields
I have seen this kind of relationship
discussed by others.
My previous example should not have the UNIQUE statement,
but it may be that you have 3 many-to-many relationships.
Message-Workgroup is M:M, Message-Hyperlink is M:M and
Hyperlink-Workgroup is M:M.
You have 3 tables and need 3 relationships to resolve them,
so, you need 6 tables.
"Mike Gramelspacher" <gr******@psci. netschreef in bericht
news:MP******** *************** *@news.psci.net ...
>>
My previous example should not have the UNIQUE statement,
but it may be that you have 3 many-to-many relationships.
Message-Workgroup is M:M, Message-Hyperlink is M:M and
Hyperlink-Workgroup is M:M.
You have 3 tables and need 3 relationships to resolve them,
so, you need 6 tables.
Thanks. I'll look into that.
john
In article <W5************ ********@casema .nl>, jo**@test.com says...
"Mike Gramelspacher" <gr******@psci. netschreef in bericht
news:MP******** *************** *@news.psci.net ...
>
My previous example should not have the UNIQUE statement,
but it may be that you have 3 many-to-many relationships.
Message-Workgroup is M:M, Message-Hyperlink is M:M and
Hyperlink-Workgroup is M:M.
You have 3 tables and need 3 relationships to resolve them,
so, you need 6 tables.
Thanks. I'll look into that.
john
Here is a small database where I tried to do multiple relations. http://www.psci.net/gramelsp/temp/Mu...s%20No%202.zip
This was just a learning thing, so take it for what it is worth.
>
"Mike Gramelspacher" <gr******@psci. netschreef in bericht news:MP******** *************** *@news.psci.net ...
My previous example should not have the UNIQUE statement,
but it may be that you have 3 many-to-many relationships.
OP stated he had two 1:M relationships
You have 3 tables and need 3 relationships to resolve them,
so, you need 6 tables.
Huh ????
Arno R
In article <45************ **********@text .nova.planet.nl >, ar***********@t iscali.nl says...
>
"Mike Gramelspacher" <gr******@psci. netschreef in bericht news:MP******** *************** *@news.psci.net ...
My previous example should not have the UNIQUE statement,
but it may be that you have 3 many-to-many relationships.
OP stated he had two 1:M relationships
You have 3 tables and need 3 relationships to resolve them,
so, you need 6 tables.
Huh ????
Arno R
Yes, but I inferred there could really be 3 relationships.
Maybe the inference was wrong. It happens regulary. I wonder
what entity is the recipient of these messages. A message
has a hyperlink that relates to a workgroup, but the message
itself does not. The workgroup does not need the message,
but only the hyperlink. OK. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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