Advice on table design which will allow me to enforce integrity

[obhayes]

Hi,
I have two tables Table A and B, below with some dummy data...

Table A (contains specific unique settings that can be requested)

Id, SettingName
1, weight
2, length

Table B (contains the setting values, here 3 values relate to weight
and 1 to length)

Id, Brand, SettingValue
1, A, 100
1, B, 200
1, null, 300
2, null, 5.3

(There is also a list of Brands available in another table). No primary
keys / referential integrity has been setup yet.

Basically depending upon the Brand requested a different setting value
will be present. If a particular brand is not present (signified by a
null in the Brand column in table B), then a default value will be
used.
Therefore if I request the weight and pass through a Brand of A, I will
get 100
If I request the weight but do not pass through a brand (i.e. null) I
will get 300.

My question is, what kind of integrity can I apply to avoid the user
specifying duplicate Ids and Brands in table B. I cannot apply a
composite key on these two fields as a null is present. Table B will
probably contain about 50 rows and probably 10 of them will be brand
specific. The reason its done like this is in the calling client code I
want to call some function e.g.
getsetting(weight) .... result = 300
Or if it is brand specific
getsetting(weight,A) ..... result = 100

Any advice on integrity or table restructuring would be greatly
appreciated. Its sql 2000 sp3.
Thanks
brad

[David Portas]

As you have already realized, TableB isn't even in First Normal Form.
Attribute Value models like this are seldom viable and you haven't
stated any excuse not to use the standard, normalized approach:

CREATE TABLE TableB (id INTEGER NOT NULL, brand CHAR(1) DEFAULT 'Z' NOT
NULL REFERENCES Brands (brand), weight INTEGER NOT NULL, length INTEGER
NOT NULL, PRIMARY KEY (id,brand))

Either add the default ("Z" here) brand to the brands table, or if you
prefer not to do that, put the brand-specific info into a separate
table:

CREATE TABLE TableB (id INTEGER NOT NULL, default_weight INTEGER NOT
NULL, default_length INTEGER NOT NULL, PRIMARY KEY (id))

CREATE TABLE TableBBrands (id INTEGER NOT NULL REFERENCES TableB (id),
brand CHAR(1) NOT NULL REFERENCES Brands (brand), weight INTEGER NOT
NULL, length INTEGER NOT NULL, PRIMARY KEY (id,brand))

Personally, I would lean toward the former design. This meets all the
requirements that you have specified as far as I can see.

--
David Portas
SQL Server MVP
--

[strider5]

i would go with two tables B1(id ,brand , value) with PK (id,brand) and
B2(id,value) PK (id)
but i think that more appropriate solution is to have separate table
for each "setting type" e.g.
WEIGHTS, LENGTHS, VOLUMES where you can have appropriate data type for
each setting

HTH, Strider

[David Portas]

> i think that more appropriate solution is to have separate table

for each "setting type" e.g.
WEIGHTS, LENGTHS, VOLUMES

Do you mean separate COLUMNS? Why would you create separate tables for
each attribute?

--
David Portas
SQL Server MVP
--

[obhayes]

I should have also said that Table A will grow in size over time (i.e.
60 different settings), so you can have many settings, i.e. a user
could add additional settings in here, therefore making these as
columns would not be ideal. If possible I would also prefer to not have
to have a dummy brand.

David Portas wrote:

i think that more appropriate solution is to have separate table
for each "setting type" e.g.
WEIGHTS, LENGTHS, VOLUMES
Do you mean separate COLUMNS? Why would you create separate tables

for each attribute?

--
David Portas
SQL Server MVP
--

[strider5]

>Why would you create separate tables for

each attribute?

i don't know, perhaps transient brain disorder ;)

[David Portas]

Why can't you implement the necessary change control procedures to add
columns as the users require them? Allowing users the unfettered
ability to add new "attributes" to a system is a recipe for creating an
unusable mass of redundant and inconsistent data. Do you really expect
users to go through the process of identifying and eliminating
functional dependencies before they add new attributes? On the whole,
users aren't good database architects. At least if they were they would
work with proper tables and columns, constraints and keys - things
which aren't possible under your model.

Your question was how to enforce integrity but I don't see any
integrity in your design at all.

--
David Portas
SQL Server MVP
--

[obhayes]

Yup, I agree all valid points there David. Thanks for your input on
this one.
Brad
David Portas wrote:

Why can't you implement the necessary change control procedures to add columns as the users require them? Allowing users the unfettered
ability to add new "attributes" to a system is a recipe for creating an unusable mass of redundant and inconsistent data. Do you really expect users to go through the process of identifying and eliminating
functional dependencies before they add new attributes? On the whole,
users aren't good database architects. At least if they were they would work with proper tables and columns, constraints and keys - things
which aren't possible under your model.

Your question was how to enforce integrity but I don't see any
integrity in your design at all.

--
David Portas
SQL Server MVP
--

[--CELKO--]

1) Please post DDL, so that people do not have to guess what the keys,
constraints, Declarative Referential Integrity, datatypes, etc. in your
schema are. Sample data is also a good idea, along with clear
specifications.

2) Google EAV and attribute splitting" design flaws before you destroy
your database. It is virtually impossible to have any data integrity
with this "design" becuase of the need to write a complete RDBMS engine
in SQL constraints.

3) The thing falls apart in about one year of operation. That is based
on fixing these things as a consultant.

4) You need help from someone who knows even a little bit about data
modeling. You have not even gottent o the basic normal forms yet.

[Erland Sommarskog]

[posted and mailed, please reply in news]

(ob*****@hotmail.com) writes:

My question is, what kind of integrity can I apply to avoid the user
specifying duplicate Ids and Brands in table B. I cannot apply a
composite key on these two fields as a null is present. Table B will
probably contain about 50 rows and probably 10 of them will be brand
specific. The reason its done like this is in the calling client code I
want to call some function e.g.
getsetting(weight) .... result = 300
Or if it is brand specific
getsetting(weight,A) ..... result = 100

I would add a dummy primary key to TableB, possibly an IDENTITY column.
When I would add a UNIQUE constraint on (Id, Brand). A UNIQUE constraint
does permit for NULL values, but only one NULL.

(It's a bit amazing that a thread with so many replies did not include
this simple and straigtforward suggestion.)
--
Erland Sommarskog, SQL Server MVP, es****@sommarskog.se

Books Online for SQL Server SP3 at
http://www.microsoft.com/sql/techinf...2000/books.asp