Re: When does one put data into a separate table?

Paul wrote: 

This is a sort of vague question.


Let's say that you have a db with a "personnel" table.

Personnel_ID INTEGER PRIMARY KEY,
First_Name    VARCHAR(30) NOT NULL,
Last_Name    VARCHAR(50) NOT NULL,
add1..
add2..
add3...
tel..
mobile...
Language1  VARCHAR(25) NOT NULL,
Language2  VARCHAR(25),
Language3  VARCHAR(25),



Now, my question here is when does it become necessary to hive off
another table 

Person_Language
ID INTEGER NOT NULL
Language VARCHAR(25) NOT NULL


The vast *_vast_* majority of people will only speak one or two, a few
3, a couple 4 and very, very few will speak 5 or more. So, let's say
we allow 5 fields in the Language part of the table, or even 6 or 7
(just to cover the Einsteins). 

I'm wondering when people would both in theory and/or in practice
start to move an attribute like this off into another table? Is there
a "Golden Number" above which it automatically gets put into another
table, or how do IT professionals decide on such things?


Paul...




here's a vague answer then. 1) be wary of what professionals do as the term only means somebody else has decided to pay them, who knows who and for who knows what reason, and the result may not be very good/useful, which may be why so many professionals seem to be needed. 2) as to the point, i'd say you could try to decide/find out how the language info is going to be used. for example, if the purpose of one of the languages is to know which to use when communicating with an employee, then that sounds like one 'primary' 'field'. if the others are there for biographical reasons or to know if somebody can help out in Russia, then you might get away with a single 'secondary/alternate' field. seven language fields seems a bit much to me. besides, you might end up deciding that a better way to record language is as an attribute of work people have done in the past, which would possibly be held in one or more different tables than the personnel ones.

p


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