The world's most popular open source database
MySQL 5.4 provides support for precision math: numeric value handling that results in extremely accurate results and a high degree control over invalid values. Precision math is based on these two features:
SQL modes that control how strict the server is about accepting or rejecting invalid data.
The MySQL library for fixed-point arithmetic.
These features have several implications for numeric operations:
Precise calculations: For
exact-value numbers, calculations do not introduce
floating-point errors. Instead, exact precision is used. For
example, a number such as
.0001 is treated as
an exact value rather than as an approximation, and summing it
10,000 times produces a result of exactly
not a value that merely “close” to 1.
Well-defined rounding behavior:
For exact-value numbers, the result of
ROUND() depends on its argument,
not on environmental factors such as how the underlying C
Platform independence: Operations on exact numeric values are the same across different platforms such as Windows and Unix.
Control over handling of invalid
values: Overflow and division by zero are detectable
and can be treated as errors. For example, you can treat a value
that is too large for a column as an error rather than having
the value truncated to lie within the range of the column's data
type. Similarly, you can treat division by zero as an error
rather than as an operation that produces a result of
NULL. The choice of which approach to take is
determined by the setting of the
sql_mode system variable.
An important result of these features is that MySQL 5.4 provides a high degree of compliance with standard SQL.
The following discussion covers several aspects of how precision
math works (including possible incompatibilities with older
applications). At the end, some examples are given that demonstrate
how MySQL 5.4 handles numeric operations precisely. For
information about using the
sql_mode system variable to control
the SQL mode, see Section 5.1.8, “Server SQL Modes”.