DSXchange

we are maintaining the history in type2. for primary key value we are using surrogate key.

but in one interview he asked why u preferred surrogate key than the primary key and tellme the what is the difference b/w Surrogate key and primary key

And what was your reply?

Have you searched here, Google, Wikipedia and/or The Data Warehousing Institute (to name a few) for the rationale of using surrogate key in Type 2 SCD?

both enforce uniqueness to the record although SK is generated for only newly inserted records in the database based on some key columns.

In type 2 we simply insert the a new record based on a history handling column rather than updating it. Space would be an issue in type 2 as we are inserting multiple records for the same person for example.

Correct me if i am wrong?

Hi,

sorrogate key used to preserve referal integrity, tht's the answer!

But it's the wrong answer.

A surrogate key preserves uniqueness, nothing more.

When you need to preserve history, such as to be able to track a person's name or address changes, then the primary key of PersonID alone won't do it. You'd need a primary key made up of PersonID and some way of identifying which is the current record, such as effective date and maybe an "is active" flag. Already the key structure is cumbersome. Instead, load this information into (possibly indexed) non-key columns and assign a surrogate, or artificial key. Integer is usually chosen as the data type, because these join very easily. However, SQL Server offers a GUID data type with similar characteristics, for example.

Hi,

Surrogate key is a substitution for the natural primary key. It is just a
unique identifier or number for each row that can be used for the
primary key to the table. The only requirement for a surrogate primary
key is that it is unique for each row in the table. It is useful because
the natural primary key can change and this makes updates more
difficult.Surrogated keys are always integer or numeric.

Thx
AjayD

Didn't realize there was a Google contest going on.

Surrogate key is a substitution for the natural primary key. It is just a unique identifier or number for each row that can be used for the primary key to the table. The only requirement for a surrogate primary key is that it is unique for each row in the table.

http://datawarehouse.ittoolbox.com/docu ... e-key-1501#

Interesting how many 'interview answer sites' have this exact same phrase ( including substitution rather than substitute) indicating massive copying from the ITToolBox source.