Oracle 5.0 Reference Manual page 1023

range of such literals differs from before. (Prior to MySQL 5.0.3, decimal values could have up to
254 digits. However, calculations were done using floating-point and thus were approximate, not
exact.) This change in the range of literal values is another possible source of incompatibility for older
applications.
Values for columns no longer are represented as strings that require 1 byte per digit or sign
DECIMAL
character. Instead, a binary format is used that packs nine decimal digits into 4 bytes. This change
to storage format changes the storage requirements as well. The storage requirements for
DECIMAL
the integer and fractional parts of each value are determined separately. Each multiple of nine digits
requires 4 bytes, and any remaining digits require some fraction of 4 bytes. The storage required for
remaining digits is given by the following table.
Leftover Digits
0
1–2
3–4
5–6
7–9
For example, a
DECIMAL(18,9)
integer part and the fractional part each require 4 bytes. A
integer digits and six fractional digits. The integer digits require four bytes for nine of the digits and 3
bytes for the remaining five digits. The six fractional digits require 3 bytes.
As a result of the change from string to numeric format for
no longer store a leading
into a
+0003.1 DECIMAL(5,1)
3.1. For negative numbers, a literal
behavior must be modified to account for this change.
The change of storage format also means that
extension that permitted values larger than the range implied by the column definition. Formerly, 1
byte was allocated for storing the sign character. For positive values that needed no sign byte, MySQL
permitted an extra digit to be stored instead. For example, a
range of at least
–999
using the sign byte to store an extra digit. This extension to the upper range of
no longer supported. As of MySQL 5.0.3, a
left of the decimal point. This can result in an incompatibility if an application has a reliance on MySQL
permitting "too-large" values.
The SQL standard requires that the precision of
DECIMAL(M,D), the standard requires a precision of at least
and
DECIMAL(M,D) NUMERIC(M,D)
Summary of incompatibilities:
The following list summarizes the incompatibilities that result from changes to
value handling. You can use it as guide when porting older applications for use with MySQL 5.0.3 and
up.
• For DECIMAL(M,D), the maximum
• Calculations involving exact-value decimal numbers are accurate to 65 digits. This is fewer than
the maximum number of digits permitted before MySQL 5.0.3 (254 digits), but the exact-value
precision is greater. Calculations formerly were done with double-precision floating-point, which has
a precision of 52 bits (about 15 decimal digits).
• The nonstandard MySQL extension to the upper range of
Data Type Changes
DECIMAL
column has nine digits on either side of the decimal point, so the
or character or leading
+ -
column, it was stored as +0003.1. As of MySQL 5.0.3, it is stored as
character is no longer stored. Applications that rely on the older
-
to 999, but MySQL would permit storing values from
DECIMAL(M,D)
are the same, and both have a precision of exactly
is 65, not 254.
M
1003
Number of Bytes
0
1
2
3
4
DECIMAL(20,6)
storage,
DECIMAL
digits. Before MySQL 5.0.3, if you inserted
0
columns no longer support the nonstandard
DECIMAL
DECIMAL(3,0)
column permits at most
be exactly
NUMERIC(M,D)
digits but permits more. In MySQL,
M
DECIMAL
column has fourteen
columns
DECIMAL
column must support a
to as well, by
1000 9999
columns is
DECIMAL
- digits to the
M D
digits. For
M
digits.
M
column and
DECIMAL
columns is no longer supported.