CODEWITHSUNDEEP
sql-serverdatabase-normalization
Royi Namir
Royi Namir

Reputation: 148524

Redundant data in sql server?

Let's say Microsoft has many CDs and it needs to track (including history) the location of each CD .

So there will probably be a CDs table like : 

CD_ID  | title | ...
_________________________
  ...  | ...   | ...

And another table which represents the "moves" : 

CD_ID  | dateMoved | DestinationCountryID |
___________________________________________
  ...  |   ...     | ...

And here is my problem :

If Microsoft wants to know where is cd Y is currently at :

It can scan the moves table and get its last county.

But ( and here is my question) :

Something inside my head tells me that I should add a column to the CDs table to be like this : 

CD_ID  | title | CurrentCountryID | ...
________________________________________
  ...  | ...   |          ...     | ...

So it would be more descriptive per Cd Item. (and easy to find).

The CurrentCountryID will be updated after each move.

But

This will cause redaundant data !

cuz now we have 2 places which represents its current location.

Am I right ? should I add this column ?

(NB if you gonna ask about quantity : lets say we have millions of cd's)

Upvotes: 0

Views: 1100

Answers (1)

Szymon
Szymon

Reputation: 43023

What you should do really depends on your needs. If you're going to look up the current country often and performance needs to be good, I would put the current country on the CDs table. Otherwise you will have to query the moves table every time and get the max date - not very good for performance.

If, on the other hand, you rarely need that information, I would normalise it and leave it only in moves table.

Upvotes: 2

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