Hi,
Here is a page from Oracle7 Server Concepts Manual.
This clearly shows how Oracle stores Numerics and Its storage sizes.
Internal Numeric Format
Datatypes 6–5 Input Data Specified As Stored As
7,456,123.89 NUMBER 7456123.89
7,456,123.89 NUMBER(*,1) 7456123.9
7,456,123.89 NUMBER(9) 7456124
7,456,123.89 NUMBER(9,2) 7456123.89
7,456,123.89 NUMBER(9,1) 7456123.9
7,456,123.89 NUMBER(6) (not accepted, exceeds precision)
7,456,123.89 NUMBER(7,–2) 7456100
Table 6 – 1 How Scale Factors Affect Numeric Data Storage
If you specify a negative scale, Oracle rounds the actual data to the
specified number of places to the left of the decimal point. For example,
specifying (7,–2) means Oracle should round to the nearest hundredths, as
shown in Table 6 – 1.
For input and output of numbers, the standard Oracle default decimal
character is a period, as in the number “1234.56”. (The decimal is the
character that separates the integer and decimal parts of a number.) You can
change the default decimal character with the parameter
NLS_NUMERIC_CHARACTERS. You can also change it for the duration of a session
with the ALTER SESSION statement. To enter numbers that do not use the
current default decimal character, use the TO_NUMBER function.
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. (However, there are only 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
THIS IS CHAPTER 6 OF ORACLE7 SERVER CONCEPTS MANUAL.
Ketan Shah.
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Received on Fri Mar 06 1998 - 00:00:00 CST
