Need Help! Can you please answer some of my questions. Thanks very much in advance!

Question

Need Help! Can you please answer some of my questions. Thanks very much in advance!

trishdiep

SSC Enthusiast

Points: 196
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July 14, 2010 at 8:45 pm

#73687

1. When you have several external databases with the same layout, how would you move them into a datawarehouse?
2. What method would you use to load data into datawareshouse with existing table that has index/constrains?
3. what benefit and why would you denormalize a table?

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Gail Shaw SSC Guru Points: 1004504 More actions · Answer 1

Homework? Interview questions?

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

trishdiep SSC Enthusiast Points: 196 More actions · Answer 2

Hello Gail Shaw,

Thanks for your response and your anwer in advance!...You've always been a fan of mine! I am preparing for my interview questions...

Gail Shaw SSC Guru Points: 1004504 More actions · Answer 3

Then may I suggest you do your own research and ask for clarifications here if necessary. Google's a great tool.

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

trishdiep SSC Enthusiast Points: 196 More actions · Answer 4

Thanks everyone for your responses! Much appreciated!

I went for an interview and it seems like they were looking for a different answers...so I just want to see your responses on these topics...

Thanks for your detailed explanation and definitely learn from it. Some folks actually say it's not good to practice the normalization...so I'm trying to get good practice and I am confused...Normalization in terms of merging some small tables that have redundant data into big tables, so doing that we could be deleting one of the table but then remember there are other applications/store procedures, components, external tools point to that table (that we just delete it), then an error will occur. We then have to worry about the clean up, so it's more risk than the benefit to do the normalization...Well I'm sure other folks have their reasons to do normalization in this aspect...

Thanks for all your responses! more thoughts?

tosscrosby SSCoach Points: 18045 More actions · Answer 5

trishdiep (7/15/2010)
Hello Gail Shaw,
You've always been a fan of mine!

Should that read "you've always been a fan of hers"??

-- You can't be late until you show up.

siddforuall SSC Journeyman Points: 77 More actions · Answer 6

Well I am new to this and would like to answer one of the questions asked.

Why do we Denormalize the tables?

Normalization is used in Relational Databases. Relational Databases main concept is to avoid data redundancy. So normalization is used to do that and this makes RDB's slow. When coming to a data warehouse main focus is on the data retrieval, faster data access. To achieve this tables are De-normalized.

Note:

To all gurus in herem, I am telling what I know..If there is anything wrong in this please correct me so that I can learn.

Thanks,

Sid

GSquared SSC Guru Points: 260824 More actions · Answer 7

Normalization makes for faster updates. Denormalization can, in some cases, make for faster selects, if it's done correctly. That's really oversimplified, but if you want a more complete view on it, there are books on the subject of data warehousing that cover it in detail. I recommend reading a couple of them.

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