Re: NUMBER Storage

What is the minimum and maximum byte storage for NUMBER?

Thomas Kyte <tkyte_at_us.oracle.com> wrote:
> A copy of this was sent to Norris <johnnie_at_cooper.com.hk>
> (if that email address didn't require changing)
> On 16 Sep 1999 13:26:30 GMT, you wrote:

>>May I know the number of bytes required to store the data type:
>>
>>NUMBER
>>NUMBER (*,1)

> <quote src=concepts manual>
> Oracle stores numeric data in variable-length format. Each value is stored in
> scientific notation, with one byte used to store the exponent and up to 20 bytes
> to store the mantissa. (The resulting value is limited to 38 digits of
> precision.) Oracle does not store leading and trailing zeros. For example, the
> number 412 is stored in a format similar to 4.12 x 10 2 , with one byte used to
> store the exponent (2) and two bytes used to store the three significant digits
> of the mantissa (4, 1, 2).

> Taking this into account, the column data size for a particular numeric data
> value NUMBER (p), where p is the precision of a given value (scale has no
> effect), can be calculated using the following formula:

> 1 byte (exponent)
> + FLOOR(p/2)+1 bytes (mantissa)
> + 1 byte (only for a negative number where the number of
> significant digits is less than 38)
> _______________________
> number of bytes of data

> Zero and positive and negative infinity (only generated on import from Version 5
> Oracle databases) are stored using unique representations: zero and negative
> infinity each require one byte; positive infinity requires two bytes.

> </quote>

> So, the above 2 number formats will consume EXACTLY the same amount of variable
> space given the same input numbers.

> --
> See http://govt.us.oracle.com/~tkyte/ for my columns 'Digging-in to Oracle8i'...
> Current article is "Part I of V, Autonomous Transactions" updated June 21'st
>
> Thomas Kyte tkyte_at_us.oracle.com
> Oracle Service Industries Reston, VA USA

> Opinions are mine and do not necessarily reflect those of Oracle Corporation

-- 
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