Should surrogate key be numeric?

1. While on a data modleing course at Oracle, I was advised NOT to use numeric data types unless you needed to do numeric/arithmetic operations on the attribute. E.g. Even though an account_id is all digits it should still be declared as alpha numeric ( VARCHAR2) as it is NOT really a numeric. This makes sense.
I would like opnions on the above
2. If above advice is taken, then even a surrogate key should be alpha numeric since it does not require arithmetic/numeric computations. However, I have also heard that numerics are better than VARCHAR2 for joins. If this join performance advantage is true, then using a NUMBER data type for surrogate keys should be preferred over VARCHAR2? This overrides the advice in 1 above for join performance reasons.
I would like comments on 1 and 2.
Thanks
Edited by: user4900730 on Jun 16, 2010 12:19 PM

user4900730 wrote:
1. While on a data modleing course at Oracle, I was advised NOT to use numeric data types unless you needed to do numeric/arithmetic operations on the attribute. E.g. Even though an account_id is all digits it should still be declared as alpha numeric ( VARCHAR2) as it is NOT really a numeric. This makes sense.
I would like opnions on the above
2. If above advice is taken, then even a surrogate key should be alpha numeric since it does not require arithmetic/numeric computations. However, I have also heard that numerics are better than VARCHAR2 for joins. If this join performance advantage is true, then using a NUMBER data type for surrogate keys should be preferred over VARCHAR2? This overrides the advice in 1 above for join performance reasons.
I would like comments on 1 and 2.
Thanks
Edited by: user4900730 on Jun 16, 2010 12:19 PMSybrand gave a pretty good analysis of the performance issues. The instructor you mention just carried away with the idea of 'not everything that LOOKS like a number IS a number'. I think his point is valid for things like SSN and telephone numbers, etc. But my take is that if you are using a "number" for a surrogate key, then it probably really is a number - even if it is true you'd never do arithmetic on it. Comes back to the first lesson of being a dba (quoted in the first two minutes of the first Oracle class I took at their facility in Atalanta, back at version 7.3). "The answer to almost every question is 'it depends'"

Similar Messages

DataModeler v3.3.0 - Naming standards template for surrogate keys creation

I'm using DM 3.3.0.734 and in the logical model we now can define in the entity properties to "Create Surrogate Key".
When we use Engineer to relational model, for each entity is automatically created a new column using the naming template {entity}_ID as NUMERIC (without precision) and is defined as primary key.
My questions are:
Is possible to define a different naming standard for surrogate key creation?. We define id_{entiry}
Is possible to set the precision of NUMERIC surrogate key?
If we define entity's column as Primary UID, these columns are included in an unique constraint, but are using the naming standards for PK.
As consequence are created the following:
Unique constraint name: entity_PK
Primary key(surrogate)name: entity_PKv1
There is any way to define naming standards like "{entity}_UID" for unique constraints, or even, "{entity}_SK" for surrogate primary key name?
Can anyone help with some of these topics?
Regards,
Ariel.

Hi Ariel,
Naming standards template for surrogate keys creation I logged enhancement request for that.
How to change those bad names (going to change them one by one is not an option):
1) If those "transformed" unique keys are the only ones you have in relational model then simply can apply naming standards
2) You can write transformation script to do that for you
3) you can use new functionality - search, export to excel file, change the names there (using find/replace will be faster) and return changed data back to relational model
you can find description for that here:
https://apex.oracle.com/pls/apex/f?p=44785:24:13179871410726::NO:24:P24_CONTENT_ID,P24_PREV_PAGE:6621,16
http://www.thatjeffsmith.com/archive/2012/11/sql-developer-data-modeler-v3-3-early-adopter-search/
http://www.thatjeffsmith.com/archive/2012/11/sql-developer-data-modeler-v3-3-early-adopter-collaborative-design-via-excel/
You should search for _PK, then filter result on Index and you can export result using report functionality (to XLS or XLSX output format). You can create template and include only table and name (of index) as properties to be included into report.
Regards,
Philip

Apex and Natural Vs Surrogate keys

Hi
We've been using Apex for a few months now and there's a debate raging in our department over whether we should design our database tables using natural or surrogate (based on Oracle sequences / triggers) keys. Our experience as Apex developers shows that Apex itself looks to lean towards surrogate keys, a few examples are below:
- When creating forms on reports / tables Apex only allows 2 primary key columns without adding 'extras' in the background (see a previous post of mine).
- If we have a form on a table and our natural primary keys can be updated, the Apex-created DML statements break, as they look to do the update using the changed key values in the WHERE clause rather than the old ones. The only way around this seems to be to delete the inbuilt DML statements created by Apex and code your own, which is extra work.
- The Apex sample applications themselves seem to use sequences / surrogate keys.
What are people's opinions on this? In particular is there any guidance from the Apex development team on which is best to use with Apex?
Regards
Antilles

Hi Andrew,
As with abots_d, I only use "natural" keys for lookups.
>
1. the department names were here for 20 years and they never changed
>
But, can you guarantee that they never will? My firm has changed departmental names so many times, it's getting ridiculous! But other things also change over time - consider what happens if a person gets married and changes their name and you've used their previous names as the keys (and consider how much data in other tables may use those keys).
>
2. Server names are uniquely generated by special formula in excel to preciously avoid the duplication problem and guarantee the uniqueness within our glamorous bank.
>
SQL could probably recreate that formula and Unique Key constraints would handle the rest
>
3. no, we are not going to extend this app to cover any other banks
>
Given what's happening with the banking industry right now, who can say ;)
>
4. PK that means smth ( aka "server name" ) has a meaning, whereas meaningless - has no (business) value
>
Why does a bit of data have to have explicit "business value"? I would suggest that a surrogate key is a pointer to a record and allows you to easily create relationships. Once created, the key would never be changed regardless of what happens to the data on its record. Thus, the relationship is maintained. Using personnel (which our firm renamed as "Human Resources" a while back) as an example, it's likely that every employee would have an employee number. Does this number actually mean anything in itself, does it have "business value"? Most likely, it's just a convenient way to identify a person and relate records to them.
I would suggest that any non-numeric/date keys are relatively slow. As strings, the only way to check for their sort order would be to (A) convert to upper or lower case and (B) perform a string comparison left-to-right across the entire string. There's also the possibility of certain characters appearing in the strings that can cause issues - for example, quotes, apostrophes, colons, commas, question marks and percentage signs.
Also, consider the length of a VARCHAR2 that you would have to use - how big would it need to be to cover all possibilities? You may say 20 now but tomorrow you get data with 21 characters in it - do you want to update the table plus all related tables for that?
There are further issues with parent, child, grand-child etc relationships where the keys would have to be passed down in full through the relationships. Depending on how many levels you may have, a fair number of the fields on the bottom-most table would be there just for the keys.
It has been a standard industry practice for many years now to "normalise databases" to avoid lots of issues with keys and "repeating data". Apart from very simple lookup tables, I have stuck with those guidelines for years now without any problems at all.
Andy

Why does BW use surrogate keys ?

Hi,
can anyone answer me in 1 sentence:
Why dos BW uses surrogate / artifical keys ?
Its not faster while querying - line items are faster & y need query more tables.
Its not faster while loading - surrogate keys need to be looked up and build up.
ThanXs
Martin

A database don't care if it's numeric or not. Index access is index access and that is what matters. But talking about indexes. There is less index'es to maintain when you use surrogates, otherwise you should have an index on each characteristic in the fact table, and it could be a lot. Also there may be a historical technical reason, like the number of key fields available on a table. Remember that SAP is trying to be DB vendor independent so if a supported DB only accepts say 16 key fields, then you need to design you application for that.
-Kristian

About Surrogate Key and Dimension Key on OWB 10.2

Hi, everyone.
I am using OWB 10.2 and I have a question about Surrogate key and Dimension Key.
I indicated the foreign key as VARCHAR2 type in Fact Table and Dimension Key as VARCHAR2 type is operated as Primary key in Dimension Table. I made Single Level in Dimension Table.
I know that Dimension Key stores the surrogate ID for dimension and is the primary key of the table. Also, Surrogate ID should be only NUMBER type.
So, in this case, Surrogate ID is NUMBER type
Dimension key should be NUMBER type to store the surrogate ID.
But, Dimension key also should operate the primary to relate Foreign key as VARCHAR2 type.
How I can solve this confusing condition?
Please let me know that.
JWS

Hi JWS,
From a SQL point of view it should not be a problem to join a NUMBER field to a VARCHAR2 field because during execution there will be an implicite cast for the NUMBER value to a VARCHAR2 value. See the example below.
SELECT * FROM DUAL
WHERE 1 = '1'From an OWB point of view it is not possible to have a Dimension with an NUMBER value Key that has a relation to a VARCHAR2 value Foreign key in a Fact table. This is caused due to the creation of a Fact table in OWB in which the Foreign keys in it are build from de Dimension tables that refer to them.
You will loose the reference to the Dimension when changing the type of the Foreign Key.
To resolve this issue I would advise you to use a Sequence that generates your Surrogate Key (NUMBER type) for the Dimension table and store it in the Primary Key Column (VARCHAR2 type).
When validating the mapping you will get a warning, but when executing this should give no problems.
Regards,
Ilona

Surrogate Key and Map for Cube

Hi
I am new to Data Warehousing and am trying to use OWB 11g.
I am trying to create dimensions with multiple levels. When I create more than one level it need to have surrogate as well business key for each dimension level. But I can create only one surrogate in the dimension, there is no option to create multiple surrogate keys in the same dimension. so what am I missing?
My second question is regarding cube. Do I need to create a Mapping for a cube? if yes, should I move the data to the cube from the dimensions? and where will the measures come from? do i need to load the measures or they will be calculated automatically?
please reply...
regards
Arif

hi
Got it, Yes that was the reason,
The table was not properly deployed after the dimension was modified.
Anyway, the describe of the table is as follows
describe arif.QUESTION_DIM
Name Null Type
DIMENSION_KEY NOT NULL NUMBER
IGV_ID NUMBER
PER_ID NUMBER
DIM_ID NUMBER
IGO_ID NUMBER
INQ_ID NUMBER
ID NUMBER
DIM_ORDEM NUMBER
DIM_AMBITO VARCHAR2(3)
DIM_NOME VARCHAR2(150)
10 rows selected
Now, I am having another problem,
when, I deploy the Map to load the data from three different tables, it gives the following problem
Name               Action               Status          Log
QUESTION_MAP          Create               Warning          ORA-06550: line 297, column 25:
                                        PLS-00302: component 'ID' must be declared
QUESTION_MAP          Create               Warning          ORA-06550: line 1153, column 11:
                                        PL/SQL: SQL Statement ignored
QUESTION_MAP          Create               Warning          ORA-06550: line 1155, column 15:
                                        PL/SQL: ORA-00904: "QUESTION_DIM"."ID": invalid identifier
QUESTION_MAP          Create               Warning          ORA-06550: line 1155, column 31:
                                        PLS-00302: component 'ID' must be declared
QUESTION_MAP          Create               Warning          ORA-06550: line 233, column 1:
                                        PL/SQL: SQL Statement ignored
QUESTION_MAP          Create               Warning          ORA-06550: line 2539, column 11:
                                        PL/SQL: SQL Statement ignored
QUESTION_MAP          Create               Warning          ORA-06550: line 2541, column 15:
                                        PL/SQL: ORA-00904: "QUESTION_DIM"."ID": invalid identifier
QUESTION_MAP          Create               Warning          ORA-06550: line 2541, column 31:
                                        PLS-00302: component 'ID' must be declared
QUESTION_MAP          Create               Warning          ORA-06550: line 297, column 9:
                                        PL/SQL: ORA-00904: "QUESTION_DIM"."ID": invalid identifier
Edited by: user643560 on Oct 22, 2008 9:38 AM

Problems maintaning surrogate keys

Hi,
I am trying to load a dimension table. the initial load worked fine. now for the regular load if there is one a new record in the source table it does adds 1 new record in the dimension table. But the problem is the surrogate keys(I am using a oracle sequence for this) skips the number of record in the dimension table and assigs next value to the new record. The lode type is "insert/Update".Constraint used for maching is the primary key of source table.
e.g
--initial run.. table had 5 records before
-- Second run.. table has 6 records but the surrogate keys value for the 6th record will be '11' insted of being '6'
can you help me with this.....

Nawneet,
after I posted this problem on the forum i read an article that said i should do something like what you said. so i changed the seq to an function which returns only the next value when called. i imported it to the map and used it insted of the seq...but still no use....the map is doing the same thing during the second run. i also tried chaning the load type from insert/update to update/insert. also changed the default operating mode to row based....still no use...:((.....
what happens is during the first run 5 records get loaded perfectly and every thign is fine, but if I run it again with no new changes in the source records the map runs fine and the data is still good. but what happens is the nextval of the sequence jumps to 11...when i am expecting it to remain at 6 as no new records have been added to the dimension table. I think some how owb is seeing 5 records in the source table during the second run and uses the next val frmo the cache...but does not use them and then since it not used this values go waste.
Problem: I can not schedule the load of the dimension table for every day as the next value of this seq will keep on skeeping and when ever a new record is added to dimension table will have a large value .

Implementing surrogate keys in dimensions

hello,
First thing, I'm new to ODI! I am using Oracle data integrator 10.1.3.
I have a dimension table 'Dim_Contracts' as target table. The structure is as follows:
PK_Dim_Contract Primary key (surrogate key - to be populated from an Oracle database sequence in the target)
Contract_ID (normal field in target - no constraints in target- to be populated from source - originally a primary key in source)
+ other dimension attributes.
from what i have googled out and read in the forum, i cannot define 'PK_Dim_Contract' as the primary key of my dimension (target) table, to be able to update it from the oracle sequence defined - rather the 'contract_ID', which is the natural key should be the primary key. Is that correct? If yes, isn't it against dimension modelling principle?
More to the point, my question is: How do I populate a sequence in my primary key field in the target table?
Thanks for your help.
Regards,
Anju

Hello Anju,
Welcome in the ODI community ;).
What I suggest you is to set the UNIQUE KEY on Contract_ID in your target. This way you will be able to use flow control and do Incremental Update Loading.
PK_Dim_Contract (surrogate key) can be your primary key in the dabatase.
To populate PK_Dim_Contract from an Oracle Sequence, create it first in your Oracle DB. Add a new sequence to your project (left pane), choose Natural Sequence, choose your schema and enter the name of your Oracle Sequence.
In your interface, define the mapping of PK_Dim_Contract as
:<ODI_SEQUENCE_NAME>_NEXTVALand execute this mapping on the target.
Note: :<ODI_SEQUENCE_NAME>_NEXTVAL works only for SQL Statements. If you want to use the sequence somewhere else, use the following syntax :
#<ODI_SEQUENCE_NAME>_NEXTVALHope it helps,
Jerome

Use of Surrogate Key

In designing table, is it always safe to use surrogate key, say an NUMBER(38) type, generated by a sequence - even a naturally occuring candidate key does exist e.g. student_id?
What are the considerations when choosing the PK column(s)?

This is actually situational. Although I personally prefer to use surrogate keys whenever possible, there are valid reasons why natural keys should be preferred in some situations (such as a reference/lookup table for instance). I discuss key strategies at http://www.agiledata.org/essays/dataModeling101.html#AssignKeys and have been meaning to rework this section into its own article one of these days.
- Scott
http://www.ambysoft.com/scottAmbler.html

Hash partitioning v. list partitioning on surrogate key + partition pruning

Hi,
Have a large fact table with surrogate keys, therefore queries are of form
select dimension.attribute..
from fact, dima, dimb..
where facta.dima_surrogate_key = dima.dimension_key
and facta.dimb_surrogate_key = dimb.dimension_key
and dima.attribute = <value>
and dimb.attribute = <value>
Would ideally like partition pruning to happen but will this happen if hash partition on facta.surrogate_key
Likewise could list partition on facta.dima_surrogate_key and further sub-partition on hash of factb.dima_surrogate_key.
Any advice much appreciated.

user5716448 wrote:
Hi,
Version 11.2.0.1
fact table structure
PRODUCT_ID NUMBER
RETAILER_ID NUMBER
OUTLET_ID NUMBER
CALENDAR_ID NUMBER
BRANCH_ID NUMBER
PUBLISHER_ID NUMBER
DISTRIBUTOR_ID NUMBER
TRANS_TYPE_ID NUMBER
TRANS_QTY NUMBER (10)
TRANS_VALUE (10,4)
No date on fact table (just surrogate_id for calendar whihc links to calendar/date dimension.
Although queries can be by date of transaction, most aren't.
Potential to grow to 3 billion rows.
Considering hash partitioning on the product_id, simply to break data down and product_id is the largest dimension.About hash partitioning – in this case it is probably all about the ability to run in parallel. Do not have any info on that, so I cannot comment further.
>
sqls are varied, lots of different types some query all dimensions, sometimes a few. Not the straightforward date examples in the manual.You can pick a dimension that is frequently used by the SQLs. I understand that there is no perfect one, but even if you pick just a “good” one you might have a good deal of partition elimination.
>
Users run 3rd part ad-hoc reporting layer which has to allow them to report against the star in any way they want.
Star transformation hint enabled. Have heard in deciding number of hash partitions, partition size should geneerally be < 2gb.
e.g transactions for a given product for customers belonging to a given multiple in a given week
select trans_qty, trans_value, m.prod_name, m.prod_num, r.cust_name, w.branch_name, rtt.trans_date, rtt,trans_type
from retailer_transaction rt, media m, wholesaler w, calendar c, retailer r, trans_type rtt
where rt.issue_id = m.dimension_key
and m.prod_num = 600
and rt.branch_id = w.dimension_key
and rt.outlet_id = r.dimension_key
and r.multiple_num = 700
and rt.calendar_id = calendar.dimension_key
and m.issue_year_week = 201110
and rt.trans_type_id = rtt.dimension_keyLastly, you need to focus on weather and how to partition your indexes (I assume you have bunch of bitmaps). This decision is at least as important as partitioning the table.

Joe - Why was SURROGATE KEY left out from ISO table design?

The lack of SURROGATE KEY causes lots of confusion and ultimately loss of productivity. Common practice in SQL Server development to make the SURROGATE KEY the PRIMARY KEY, the source of all trouble because it is not really the "PRIMARY KEY" just
a meaningless integer identifier.
Example:
CREATE TABLE Products (
ProductID INT SURROGATE KEY,
ProductNumber char(12) PRIMARY KEY,
Name nvarchar(100) NOT NULL UNIQUE,
ListPrice DECIMAL (12,2) NOT NULL,
Color varchar(10) );
Is there a hope of correcting this issue?
Thanks.
Kalman Toth Database & OLAP Architect
SQL Server 2014 Database Design
New Book / Kindle: Beginner Database Design & SQL Programming Using Microsoft SQL Server 2014

Thanks Joe.
In SQL Server world we do use SURROGATE IDENTITY (or SEQUENCE object) INT in table design. That's like in our DNA even if it conflicts with Codd. AdventureWorks sample:
SELECT ProductID, ProductNumber, Name, ListPrice, Color
FROM Production.Product ORDER BY ProductNumber;
ProductID ProductNumber Name ListPrice Color
899 FR-T67Y-44 LL Touring Frame - Yellow, 44 333.42 Yellow
900 FR-T67Y-50 LL Touring Frame - Yellow, 50 333.42 Yellow
901 FR-T67Y-54 LL Touring Frame - Yellow, 54 333.42 Yellow
902 FR-T67Y-58 LL Touring Frame - Yellow, 58 333.42 Yellow
886 FR-T67Y-62 LL Touring Frame - Yellow, 62 333.42 Yellow
890 FR-T98U-46 HL Touring Frame - Blue, 46 1003.91 Blue
ProductID is the (SURROGATE) PRIMARY KEY
ProductNumber is the NATURAL KEY (created by the accounting department) - this is the real "PRIMARY KEY"
Name is the CANDIDATE KEY (too long to be a key)
In RDBMS theory when we talk about PRIMARY KEY we mean the ProductNumber column which is used in real life.
However, in reality the ProductID INT meaningless number is the PRIMARY KEY, while the meaningful ProductNumber has to settle for a UNIQUE KEY or unique index.
I understand your point that we should not use SURROGATES, but we do. It's like in our (SQL Server) blood. If I go to a company and design for them without SURROGATE IDENTITY/SEQUENCE, they would fire me. From an ORACLE forum: "Basically,
always use a surrogate key. There are a few special cases where a surrogate key really isn't any better than some "natural" key, and whatever effort is needed to create and populate a surrogate key would just be wasted. These situations
are pretty rare.
Here's one example: Say you have a many-to-many relationship between employees and departments, that is, each employee may be related to 0 or more departments, and each department may be related to 0 or more employees, but an given employee can only be
related to a given department 1 time. In that case, a primary key consisting of both columns, dept_id and emp_id, is about as good as a surrogate key. You'd need a unique constraint on (dept_id, emp_id) in any case, and I don't see any need to create a surrogate
key." LINK:
https://community.oracle.com/thread/2527771?tstart=0
I tell you Joe, 90% of the world running on SURROGATE PRIMARY KEY tables, so why should we care about Codd at this point? Even the perfect PRIMARY KEY candidate, social security number, may have problems such as stolen SSNo duplicates among others: "Natural
key. A key that is formed of attributes that already exist in the real world. For example, U.S. citizens are issued a Social Security Number (SSN) that is unique to them (this isn't guaranteed to be true, but it's pretty
darn close in practice). SSN could be used as a natural key, assuming privacy laws allow it, for a
Person entity (assuming the scope of your organization is limited to the U.S.)." LINK:
http://www.agiledata.org/essays/keys.html A good advice from the article: "Don't naturalize surrogate keys. As soon as you display the value of a surrogate
key to your end users, or worse yet allow them to work with the value (perhaps to search), you have effectively given the key business meaning. This in effect naturalizes the key and thereby negates some of the advantages of surrogate keys."
Kalman Toth Database & OLAP Architect
SQL Server 2014 Database Design
New Book / Kindle: Beginner Database Design & SQL Programming Using Microsoft SQL Server 2014

How we use Surrogate Keys for snowflake dimension

Hi All,
my question is - How we use Surrogate Keys for snowflake dimension
i heard from some body Surrogate Keys only work with star schema.
please correct me if i wrong.
Regards,
Manish

Hi manishcal16PPS,
According to your description, you can only create natural key in your dimension. But it's not working when using surrogate key. Right?
In Analysis Services, the snowflake schema of the dimensions are represented by more than one dimension table in other words its takes multiple dimension tables to define a dimension. Surrogate key are just some extra, redundant, unique key based on the
natural key. So there's no direct relationship or some limitations between surrogate keys and snowflake schema.
In this scenario, since there's relationship between the two dimensions, you should create natural key. For using natural key or surrogate key. Please refer to an article below:
Surrogate Key vs. Natural Key
For understanding star/snowflake schema, please see:
Understanding Star and Snowflake Schemas
Regards,
Simon Hou
TechNet Community Support

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).

MDX Query to show the latest product text again historical facts (Type 2 dimenion linking on Surrogate key and also Natural Key)

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.
The way I do it in TSQL is joining two queries together on the Natural Key as opposed to the surrogate key.
Can this be done in MDX. I know I could write two separate MDX queries, one which get the product text I wan and the other to get the measure with the actual product text and Natural Key, and use a lookup function in ssrs to show the two result sets I the
same tablix by looking up the Natural Keys. But this should be able to be done in one query shouldn't it.
In the dsv the fact knows to join to the dimension using the surrogate key.
Thanks J

Hi Jamster,
According to your description, you want to write a query to show the latest product text, right?
In MDX, we can use LastNonEmpty function to return the lastest member winth a dimension. LastNonEmpty is an aggregation function available in the Enterprise version of SQL Server. However, you can create your own with a little bit of recursive MDX. Here
is a sample query for you reference.
With Member Measures.LastHits as
iif(isempty(Measures.Hits),
([Date].[Year Month Day].prevmember,
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
If this is not what you want, please provide us the detail structure of your cube and the expected result, so that we can make further analysis and give you the exactly MDX query.
Regards,
Charlie Liao
TechNet Community Support

How to Maintain Surrogate Key Mapping (cross-reference) for Dimension Tables

Hi,
What would be the best approach on ODI to implement the Surrogate Key Mapping Table on the STG layer according to Kimball's technique:
"Surrogate key mapping tables are designed to map natural keys from the disparate source systems to their master data warehouse surrogate key. Mapping tables are an efficient way to maintain surrogate keys in your data warehouse. These compact tables are designed for high-speed processing. Mapping tables contain only the most current value of a surrogate key— used to populate a dimension—and the natural key from the source system. Since the same dimension can have many sources, a mapping table contains a natural key column for each of its sources.
Mapping tables can be equally effective if they are stored in a database or on the file system. The advantage of using a database for mapping tables is that you can utilize the database sequence generator to create new surrogate keys. And also, when indexed properly, mapping tables in a database are very efficient during key value lookups."
We have a requirement to implement cross-reference mapping tables with Natural and Surrogate Keys for each dimension table. These mappings tables will be populated automatically (only inserts) during the E-LT execution, right after inserting into the dimension table.
Someone have any idea on how to implement this on ODI?
Thanks,
Danilo

Hi,
first of all please avoid bolding something. After this according Kimball (if i remember well) is a 1:1 mapping, so no-surrogate key.
After that personally you could use Lookup Table
http://www.odigurus.com/2012/02/lookup-transformation-using-odi.html
or make a simple outer join filtering by your "Active_Flag" column (remember that this filter need to be inside your outer join).
Let us know
Francesco

Should surrogate key be numeric?

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