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Database design


Database design

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karthik M
karthik M
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I want to know about Database design. If we think about 'DataBase Design', which would trigger first in our mind ?

Pls dont tell 'do a search'. I am expecting some good answers from best experts.

karthik
GilaMonster
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First questions that come to mind.

What's the database for?
What's going to be stored in it, for how long and why?
Who's going to be using this and how?


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

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abmore
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Hi karthikeyan,
when we think abount DB Design the 1st trigger comes in mind is DDL trigger on database.

Trigger depends on the requirements.
Jeff Moden
Jeff Moden
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"3rd Normal Form"

Heh... Look it up Wink

--Jeff Moden

RBAR is pronounced ree-bar and is a Modenism for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column.
Although they tell us that they want it real bad, our primary goal is to ensure that we dont actually give it to them that way.
Although change is inevitable, change for the better is not.
Just because you can do something in PowerShell, doesnt mean you should. Wink

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karthik M
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whcih one should comes to mind ?

3 rd normal form
(or)
What's the database for?
What's going to be stored in it, for how long and why?
Who's going to be using this and how?
(or)
both

karthik
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absolutly correct karthikeyan, but beforeDB design we need to analyze do we really need a trigger. If yes the for what purpose we will desing it , trigger may be on table or on database (in Sql 2005 ) so it depends upon the user as well as on developer also.

If suppose DB dev. want to maintain DDL log audit on database then will write a DB trigger.
if want to maintain any table audit will create trigger on tables.
Jeff Moden
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Ahbijit,

Karthick doesn't need a "trigger"... what he said was...
I want to know about Database design. If we think about 'DataBase Design', which would trigger first in our mind ?

... and where he said "which would trigger first in our mind?", he meant "What should be the first thing we take into consideration when designing a database?

--Jeff Moden

RBAR is pronounced ree-bar and is a Modenism for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column.
Although they tell us that they want it real bad, our primary goal is to ensure that we dont actually give it to them that way.
Although change is inevitable, change for the better is not.
Just because you can do something in PowerShell, doesnt mean you should. Wink

Helpful Links:
How to post code problems
How to post performance problems
Forum FAQs
Jeff Moden
Jeff Moden
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3 rd normal form
(or)
What's the database for?
What's going to be stored in it, for how long and why?
Who's going to be using this and how?
(or)
both

Both... you cannot design a database in correct 3rd normal form without knowing the rest "what's going to be stored in it".

The "how long" and "who's going to be using this and how" actually doesn't matter much. Whether it's for a GUI or Batch File processing doesn't matter because it should always be able to do both.

If you're talking a "data mart", then that's something different. Frequently, they are both pre-summarized and somewhat "de-normalized" for performance reasons.

--Jeff Moden

RBAR is pronounced ree-bar and is a Modenism for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column.
Although they tell us that they want it real bad, our primary goal is to ensure that we dont actually give it to them that way.
Although change is inevitable, change for the better is not.
Just because you can do something in PowerShell, doesnt mean you should. Wink

Helpful Links:
How to post code problems
How to post performance problems
Forum FAQs
Matt Miller (#4)
Matt Miller (#4)
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Jeff Moden (11/26/2007)
3 rd normal form
(or)
What's the database for?
What's going to be stored in it, for how long and why?
Who's going to be using this and how?
(or)
both

Both... you cannot design a database in correct 3rd normal form without knowing the rest "what's going to be stored in it".

The "how long" and "who's going to be using this and how" actually doesn't matter much. Whether it's for a GUI or Batch File processing doesn't matter because it should always be able to do both.

If you're talking a "data mart", then that's something different. Frequently, they are both pre-summarized and somewhat "de-normalized" for performance reasons.


3NF kind of entails that you know what the "database is for". Keep in mind that the single question "what's the DB for" represents a whole (often iterative) process describing in detail what the DB is for. You need to have an idea of the breadth and depth of the data you need to collect (let's call that the "universe"); you then need to organize your universe into items that naturally go together (let's call them "entities"), and then determine how your entities should relate to each other. Then, using 3NF, you then start looking at your ENTITIES, and try to make sure that THEY don't need to be broken up and organized into more granular entities, etc...

This is not a single question anymore, as you can see. It's an intricate process, requiring involvement from both the business, dev and data areas in most cases.

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Your lack of planning does not constitute an emergency on my part...unless you're my manager...or a director and above...or a really loud-spoken end-user..All right - what was my emergency again?
GilaMonster
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Jeff Moden (11/26/2007)


The "how long" and "who's going to be using this and how" actually doesn't matter much.


I had a reason for writing those, but now I can't remember fully.

Hmmm.... Think it had to do with need for archiving and growth planning (how long). OLTP or decision support (ie, do we need to consider storing pre-computed averages, selective denormalisation, etc)

But those are more advanced concepts in DB design, and one of the biggest mistakes I see is people skipping intermediate steps to get to a final design.ie not bothering to normalise fully.


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


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