Fact vs Dimension

[karthi_gana]

All,

Which table data will be loaded first?
how many keys can be created for Fact table?
how many keys can be created for Dimension table?

Yes...This is the interview questions...one of my friend recently faced the above questions.

[SURA]

So what do you think?

FACT / DIM ?

DS User

[bskumar4u]

Fact table:It consists of foreign Keys and Measures(mostly Numeric values)
Dimension:It provides descriptive information relating to the foreign key in a fact.

Eg:- in employee table i have ename empid sal
in manager table i have mname mid and sal

so there are two dimension table
1--> emp table contains enmae eid(PK) sal
2--> Mgr table contains mname mid(PK) sal

Fact table contains
eid(FK) mid(FK) esal and msal

usually dimension tables are loaded first then fact tables followed by aggregrator tables...
there are 2 types schema in loading them:
1. Star
2. Snow flake( dimensions r broken into sub dimensions)

PLease correct me if i'm wrong..!!

[karthi_gana]

So what do you think?

FACT / DIM ?

DS User

Fact table ? I'm sorry..i am unable to fit this concepts in my projects. i have created lot of jobs..though ..i am little bit weak on this topic. I might have implemented this topic in my jobs without knowing them.

[chulett]

There's no "usually" here, only one answer as one must be loaded before the other... and the relationships between the two should make that answer obvious.

[pandeesh]

You can get a lot of info regarding Fact and Dimension by searching in "Google"..It had been discussed several times in the past .
Refer the articles by Ralph Kimball for getting more insight.

[qt_ky]

Search on Data Warehouse. If you're not doing DW work, then it will not apply so much...

[ray.wurlod]

Which will be loaded first? Whichever one you choose to load first.

However, there is a right way and a wrong way. And the wrong way is highly likely to throw errors, for example if referential integrity is enforced in the database (which it should be).

[karthi_gana]

Dimension table must be loaded first and then the fact table should be loaded.

Ref:

http://www.information-management.com/i ... gination=1

Am I correct?

[priyadarshikunal]

yes if there are foreign key constraints which should be there else it may create data integrity issues. This has been already mentioned in Craig's post.

[ray.wurlod]

Am I correct?

Not entirely. If snowflakes exist these must be loaded even before dimensions, from the outside in.