Force Natural key on a column

I know the definition of a Natural Key but I don't know how to apply it for a column. For a primary key we have a syntax like "CREATE
TABLE Persons
P_Id int NOT NULL PRIMARY KEY)"
Do we have anything similar for Natural Key?? Thanks in advance.
svk

Take a look at the Product table in AdventureWorks2012.
ProductID - INTEGER SURROGATE PRIMARY KEY
Name - UNIQUE KEY (NATURAL KEY)
ProductNumber - UNIQUE KEY (NATURAL KEY)
rowguid - UNIQUE KEY (ALTERNATE KEY)
CREATE TABLE [Production].[Product](
[ProductID] [int] IDENTITY(1,1) PRIMARY KEY,
[Name] [dbo].[Name] NOT NULL UNIQUE, -- NATURAL KEY
[ProductNumber] [nvarchar](25) NOT NULL UNIQUE, -- NATURAL KEY
[MakeFlag] [dbo].[Flag] NOT NULL CONSTRAINT [DF_Product_MakeFlag] DEFAULT ((1)),
[FinishedGoodsFlag] [dbo].[Flag] NOT NULL CONSTRAINT [DF_Product_FinishedGoodsFlag] DEFAULT ((1)),
[Color] [nvarchar](15) NULL,
[SafetyStockLevel] [smallint] NOT NULL,
[ReorderPoint] [smallint] NOT NULL,
[StandardCost] [money] NOT NULL,
[ListPrice] [money] NOT NULL,
[Size] [nvarchar](5) NULL,
[SizeUnitMeasureCode] [nchar](3) NULL,
[WeightUnitMeasureCode] [nchar](3) NULL,
[Weight] [decimal](8, 2) NULL,
[DaysToManufacture] [int] NOT NULL,
[ProductLine] [nchar](2) NULL,
[Class] [nchar](2) NULL,
[Style] [nchar](2) NULL,
[ProductSubcategoryID] [int] NULL,
[ProductModelID] [int] NULL,
[SellStartDate] [datetime] NOT NULL,
[SellEndDate] [datetime] NULL,
[DiscontinuedDate] [datetime] NULL,
[rowguid] [uniqueidentifier] ROWGUIDCOL NOT NULL UNIQUE -- ALTERNATE KEY
CONSTRAINT [DF_Product_rowguid] DEFAULT (newid()),
[ModifiedDate] [datetime] NOT NULL CONSTRAINT [DF_Product_ModifiedDate] DEFAULT (getdate()))
GO
Kalman Toth Database & OLAP Architect
SQL Server 2014 Design & Programming
New Book / Kindle: Exam 70-461 Bootcamp: Querying Microsoft SQL Server 2012

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When I load a dataset into a slowly changing dimension, sometimes the dataset contains multiple records for the same natural key. The rows are different by the column last_update_date (among other possible differences).
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Given that I'll use a natural key, how do I deal with the situation if I find out the value later?

I have been doing a lot of reading about the pros and cons of using natural versus surrogate keys. I have read in Joe Celko's books and his writing online that he strongly opposes using surrogate keys and using IDENTITY for generating values for a
surrogate key column of a table in SQL Server. I would like some advice on how to handle this situation: I have a table with physician information and would like to use their NPI as a natural key (it would be a foreign key in many other tables)
but the people who enter new physicians often don't know the NPI until later. They also may receive the wrong NPI and need to change it later.
Right now they use Excel spreadsheets to manage their data and I'm sure you can understand what a nightmare of data integrity that is. Now that I'm going to design and build a database for them, can you recommend a good approach to this specific problem?
I cannot tell them to hold on to the new physician's data until they get the NPI because they need to immediately work with the physician's information as soon as the new physician joins the organization. It's a small shop and not a health system
but thousands of physicians join. They cannot insist that the NPI be supplied at the time of registration for various political reasons. The people who are using the system now have varying degrees of skepticism to outright vehement opposition
to having a new database system so I cannot "lay down the law" about things that may adversely affect the relationship with the new physicians who sign up. With the Excel spreadsheets they cope with this by either leaving it blank, entering
9999999 or some other stray string of characters, or perhaps typing in their shopping list.
Is there a viable solution to this design problem? Any and all suggestions appreciated. Thanks for reading this.

While I disagree with the standard practice of adding an identity column as the primary key for every table, I think that this is a case where it can be beneficial or practical. You might not want to cluster on the identity column and you still need
to enforce the uniqueness of the natural key.
OTOH, the alternative is to simply fabricate a value for the natural key when it is unknown. You could do this manually (where the user must enter the fabricated value) or automatically (where the server generates it). A manual approach might
be frustrating to the users since they have to "guess" what would be unique and acceptable, resulting in sort of trial-and-error approach to adding. You would also very likely need to have a way of identifying which rows had a fabricated value. Once
the actual natural key has been identified for a given provider you would then need to update it. The server can handle cascading the value where needed if you so choose. Note that, except for the cascading part, you need the same capabilities
for an identity-based table since this natural key is most likely essential to the system.
I'll also point out that you can use a unique constraint as the target of a foreign key - you don't have to use the primary key. Not recommending this, just mentioning the alternative.
Which you should choose I can't say - that requires a much better understanding of your model and that isn't something that can be readily provided in a forum such as this. I will say that you should not prematurely choose an identity. Why? First,
you make this choice once you have deemed the natural key to be a problem. Second, it may be (at least) some of your anticipated relationships to physician are actually to something else. A medical system is as much art as science - at least in
the USA. Providers, plans, participants, terms, renewals, diagnosis codes, etc. make one's head spin. Given that you have just started modeling, there is no reason at this point to make this choice - just be aware that the natural key poses some
issues that you need to address at some point before completion. Personally I would choose the natural key for now and let the model develop and demonstrate where this choice becomes a problem.

Replacing natural keys with surrogate keys

Hi,
We have database that is runnig with some old applications since many years. In the database, all the primary key are natural keys (composed with many columns). The applications are developped with mod pl/sql and oracle forms6i / designer6i.
We are planning to develop a new system (replacing all the old applications), the database tables will ramain the same but we are thinking about replacing the natural keys with surrogate keys. Since we are planning to develop and migrate into the new system gradually (oracle forms applications will not be redeveloped first), my question is:
- will the oracle forms applications still works?
- what is the risk and precautions to take ?
- is the decision to convert natural keys into surrogate a good one?
All your comments and propositions are welcome.
Thanks.

Surrogate keys in general is a good idea. Many generators cannot handle multiple column PK's very well, or not at all. I believe, for instance, that Apex can handle 2 columns only.
But, doing this on an existing datamodel can be a lot of work. You have to change your tables, of course, but also the foreign keys, triggers, constraints etc. A PK is protected from an update, but I guess you also want your old, natural PK, to be protected as well.
Forms generates master-detail synchronization based on FK relations. If these change, you may have to change your Forms too. As long as you don't do anything in your existing form, my guess is that it will still work. The forms will maintain the FK relation between old table definitions. This works independently of the actual FK relation in the database. You can create triggers on the tables to actually populate the new PK and FK.
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Surrogate Keys vs. Natural Keys

Hi All,
Is anyone aware of a recommendation regarding the use of surrogate keys vs. natural keys?
Regards,
Irfan Abdul Rehman

The Natural Keys approach was first. This was the approach used when Relational Databases were first discovered. But I believe, it was based on the premise that the design of the Database does not change over time. Most people seem to side with one or the other. People's opinions here are usually based on what they were brought up with or personal experiences where they have run into problems with one approach or the other.
When viewed within the context of object-oriented design, the Surrogate approach is more common. Consider: does the uniqueness of a table have any relevance to other tables? If the uniqueness of a table changes, why should this have to impact other tables? If a customer is associated with an Order, using Natural Keys, you need to know what columns make the Customer unique when inserting a record into the ORDERS table. With Surrogate Keys, you don't need to know what columns make the Customer unique, the customer is referenced by its Surrogate Key. With Surrogate Keys, you only need to know what makes a Customer unique when dealing with the CUSTOMERS table.
With SQL Server, the Surrogate approach is very straight forward. In Oracle, the appeal of Surrogate Keys is less than with SQL Server as there is a more work to implement them. In SQL Server you specify the Column as an identity column. In Oracle you need to additionally add a sequence. In addition, if you want the value automatic on inserts, you will need to create a trigger (unfortunately here, when you insert, there is no way to find out what you just inserted). If you don't choose to have the value automatic on inserts, your insert SQL statements will require extra SQL code and the Surrogate value is not enforced (i.e. someone could enter any value and this could lead to a Key Violation)
Here are some disadvantages of Natural Keys:
-     Almost always, more columns to join on. If Table B is a detail table of master A and C is a detail to B and D is a detail to C, you will need at least 3 columns to join D to C in an SQL query.
-     If your uniqueness of a table changes (Ex: the number of Columns making your Table unique changes from 2 to 3), with Natural Keys, all of your SQL (Stored Procedures, Reports, Views, SQL Scripts, Application Code) will have to be re-written and your foreign keys relating to that table will have to be changed. With Surrogate Keys usually as simple as modifying that table.
-     If the data type of a Primary Key column changes (Ex: you used a varchar(20), now it's not big enough and has to be changed to varchar(100)), with Natural Keys, all Foreign Keys related to that Table will have to be changed (may also impact SQL Code). With Surrogate Keys usually as simple as modifying that table.
-     The Classic: a value changes in the Primary Key (Like Last Name). Now you've got to update that in every Foreign Key. Which means you'll have a big headache when you have to temporarily drop the constraint(s).

Table creation from type - Primary key with 2 columns

Hello,
I have to create a table from a type that I created.
The thing is that I want to create a primary key using two column.
Because this table is junction table.
How can I do this ?
CREATE TABLE CONTENT OF CONTENT_T (ID_COMP primary key, ID_CHAR_J NOT NULL PRIMAR
Y KEY);
Oracle return:
CREATE TABLE CONTENT OF CONTENT_T (ID_COMP primary key,ID_CHAR_J NOT NULL PRIMARY KEY)
ERROR at line 1:
ORA-02260: table can have only one primary key
So I tried:
CREATE TABLE CONTENT OF CONTENT_T (ID_COMP,ID_CHAR_J NOT NULL PRIMARY KEY)
ERROR at line 1:
ORA-02338: missing or invalid column constraint specification
Tahnk's in advance.
Edited by: user8266437 on 29 avr. 2009 13:56
Edited by: user8266437 on 29 avr. 2009 13:56

SCOTT@orcl_11g> CREATE OR REPLACE TYPE content_t AS OBJECT
2    (id_comp    NUMBER,
3      id_char_j VARCHAR2 (10),
4      other_cols VARCHAR2 (10));
5 /
Type created.
SCOTT@orcl_11g> CREATE TABLE CONTENT OF CONTENT_T (PRIMARY KEY (ID_COMP, ID_CHAR_J))
2 /
Table created.
SCOTT@orcl_11g> INSERT INTO content VALUES (content_t (1, 'A', 'WHATEVER'))
2 /
1 row created.
SCOTT@orcl_11g> COMMIT
2 /
Commit complete.
SCOTT@orcl_11g> INSERT INTO content VALUES (content_t (1, 'A', 'DUPLICATE'))
2 /
INSERT INTO content VALUES (content_t (1, 'A', 'DUPLICATE'))
ERROR at line 1:
ORA-00001: unique constraint (SCOTT.SYS_C0062057) violated
SCOTT@orcl_11g> COMMIT
2 /
Commit complete.
SCOTT@orcl_11g> SELECT * FROM content
2 /
   ID_COMP ID_CHAR_J OTHER_COLS
         1 A          WHATEVER
SCOTT@orcl_11g>

Explain me about natural key

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Thanks in Advance.

Hi ,
Check the below link
http://gerardnico.com/wiki/data_modeling/key
Thanks,
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wrap a view around your table with this bogus primary key. Use an instead of trigger to handle the inserts and updates. And then look at using surrogate keys to resolve these bad design issues...
5 out of 4 people don't understand fractions.
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Webster, TX

No matching unique or primary key for this column-list --error

CREATE TABLE CUSTOMER(CUS_NUM NUMBER(10) PRIMARY KEY,CUS_NAME VARCHAR2(50),ADDRESS VARCHAR2(50));
CREATE TABLE ITEM(ITEM_NUM NUMBER(10),ITEM_DESC VARCHAR2(50),TYPE VARCHAR2(50),ITEM_STATUS VARCHAR2(50),
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PRIORITY VARCHAR2(50),ORDER_STATUS VARCHAR2(50),
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For your own sanity, you should learn to format your code, or use a tool to do it for you. For the sanity of the forum members, you should preserve that code using the \ tagsCREATE TABLE CUSTOMER
CUS_NUM NUMBER(10) PRIMARY KEY,
CUS_NAME VARCHAR2(50),
ADDRESS VARCHAR2(50)
CREATE TABLE ITEM
ITEM_NUM NUMBER(10),
ITEM_DESC VARCHAR2(50),
TYPE VARCHAR2(50),
TYPE is a reserved word. Call it ITEM_TYPEITEM_STATUS VARCHAR2(50),
CONSTRAINT PK_ITEM PRIMARY KEY(ITEM_NUM,TYPE)
CREATE TABLE ITEM_TYPE
TYPE VARCHAR2(50) PRIMARY KEY,
again, with the reserved word.TYPE_NAME VARCHAR2(50),
SKU VARCHAR2(50),
RATING VARCHAR2(50)
CREATE TABLE ORDERS
ORDER_NUMBER NUMBER(10),
be consistent. NUM or NUMBER. Pick one and stick with it.CUS_NUM NUMBER(10),
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ORDER_POINT VARCHAR2(50),
DISPATCH_POINT VARCHAR2(50),
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How to implement SCD when a natural key gets changed?

Hi,
I have an requirement that, some times the natural key field of the dimension table may get changed. In that scenario, how can I implement the SCD type 2 for that dimension table. Pls post your suggestions and feedback.
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could you please be a little bit more specific and provide an example? I really can't imagine why a natural key should change. If it changes it's another item that has nothing to do with the item described by the old natural key. What I'm trying to say is if your natural key gets "broken" then it's not your natural key. Try to build one on your own. You can for instance concatenate the old natural key with a sequence number and use that construct as your natural key.
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Thanks

Hello,
I think, the way of handling multiply changes of NK is totally depend on business requirements for your project.
There could be number of approaches for this. For example:
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I need to write a MDX query to show the latest product text again historical facts or a chosen product text in time. I can write this query in TSQL, but new to MDX.
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According to your description, you want to write a query to show the latest product text, right?
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With Member Measures.LastHits as
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Measures.LastHits
),Measures.Hits)
Reference
http://cwebbbi.wordpress.com/2011/03/24/last-ever-non-empty-a-new-fast-mdx-approach/
http://richardlees.blogspot.com/2010/07/getting-last-non-empty-value.html
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Charlie Liao
TechNet Community Support

Force Natural key on a column

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