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Weight of data types [message #302579] Tue, 26 February 2008 04:06 Go to next message
n_de_fontenay
Messages: 33
Registered: October 2006
Location: Paris
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Good morning,

I'm trying to find information on how much every oracle data type weight in a database.

For example, when I put a date in a table how much does it weight.

I need to know this or a bit more generally, how are they stored in the DB.

I know that characters are 1 byte but I wonder if integers are binaries and the number 2 would be 2 bits.

I have no idea for dates and decimal numbers.

Does anyone know about those things.

A link to the subject would be great too.

regards and thanks in advance,

Nico

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Re: Weight of data types [message #302583 is a reply to message #302579] Tue, 26 February 2008 04:21 Go to previous messageGo to next message
Michel Cadot
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DBA_TAB_COLUMNS.DATA_LENGTH.

Regards
Michel

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Re: Weight of data types [message #302587 is a reply to message #302579] Tue, 26 February 2008 04:30 Go to previous messageGo to next message
n_de_fontenay
Messages: 33
Registered: October 2006
Location: Paris
Member
Hi.

this is the data_length (how long) of every columns for every table.

I'm not talking about column size here, it's really how much space in bits or bytes a value of a certain type takes on the hard disk.

and I need to know that for:
date
float
integer
varchar2

Lobs are another subject.

How are they encoded?

at school i've learned counting in binaries for integer

0
1
10
11
100
101
110
111
1000

Does that apply for integers in the DB? what about dates and floats?

this is what I have in mind.

Nico

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Re: Weight of data types [message #302598 is a reply to message #302587] Tue, 26 February 2008 05:04 Go to previous messageGo to next message
Michel Cadot
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You can't have this information for a general answer.
The best you can have is data_length.
Otherwise, for current data, you can use vsize function.

Number are coded in proprietary format, no relation with binary.
Float, integer and other are NUMBER data type.

Date are 7 bytes long, for other time type use data_length.
And so on.

Regards
Michel

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Re: Weight of data types [message #302615 is a reply to message #302579] Tue, 26 February 2008 06:17 Go to previous messageGo to next message
n_de_fontenay
Messages: 33
Registered: October 2006
Location: Paris
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I have found an awesome document explaining the generalization!

http://download.oracle.com/docs/cd/B28359_01/server.111/b28318/datatype.htm#i2093

I stick that here for posterity.

The information it seems is hard to get.

I hope to save others time like that. Spread the word!!!

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Re: Weight of data types [message #302619 is a reply to message #302615] Tue, 26 February 2008 06:38 Go to previous messageGo to next message
Michel Cadot
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This document exists in each and every Oracle version.
It does not generalize anything and don't answer the question of "what is the number of bytes used by 12456000?".
For numbers, it gives the "good old" approximative and arbitrary formula.

Regards
Michel

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Re: Weight of data types [message #302622 is a reply to message #302579] Tue, 26 February 2008 06:45 Go to previous messageGo to next message
n_de_fontenay
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Registered: October 2006
Location: Paris
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It gives a few answer and when it's not possible to give the value for a given number, it does give a formula and that's generalizaton.

I can't really use this kind of formula because I'm writing a document for a crowd of not so technical people but it does tell me that it's best having numbers in number type rather than char because the latter would weight heavier;

I need validation and sources and that will do Smile

Thanks anyway

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Re: Weight of data types [message #302629 is a reply to message #302622] Tue, 26 February 2008 06:52 Go to previous messageGo to next message
Michel Cadot
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Quote:
it does tell me that it's best having numbers in number type rather than char

Oh! If this was the root question, you should post it, I could answer you immediately.
Bytes are not the only point.
Query performances depend on optimizer understanding which relies on your datatype. Numbers are not strings, they are used differently, they have not the same range of values and behaviours.
Otherwise, why not store all data in strings? Why bother with other datatypes? (And this what some do naming this generic model Sad )

Regards
Michel

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Re: Weight of data types [message #302632 is a reply to message #302579] Tue, 26 February 2008 06:56 Go to previous messageGo to next message
n_de_fontenay
Messages: 33
Registered: October 2006
Location: Paris
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believe it or not, I got an application that my company bought (a year before, I just joined) and of course now it wreck havocs and it does mix a lot of different values in just one field called "value".

of course there's a field with an ID which links to another table called "LABEL". I thought only beginners student could do that; It seems not.

Problem is my management don't even understand why having 115 lines for a policy is wrong!!!

I have to justify everything I say and it drives me crazy!
I know why we use types, I just couldn't find something official to justify it.

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Re: Weight of data types [message #302642 is a reply to message #302632] Tue, 26 February 2008 07:35 Go to previous messageGo to next message
Michel Cadot
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Quote:
believe it or not,

I believe you, I saw it!

Quote:
I know why we use types, I just couldn't find something official to justify it.

I don't there is anything "official" as everything is in the end bits.
It is just 101 good programming practice: http://computerprogramming.suite101.com/article.cfm/datatypes or http://en.wikipedia.org/wiki/Data_type.
In Oracle, optimizer knows what is a datatype and its behaviour changes with it.

Regards
Michel

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Re: Weight of data types [message #302648 is a reply to message #302632] Tue, 26 February 2008 08:06 Go to previous message
pablolee
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Registered: May 2007
Location: Scotland
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Have a read here

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