Spec-Zone .ru
спецификации, руководства, описания, API
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Spec-Zone .ru
спецификации, руководства, описания, API
|
MySQL 5.7 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 and provide a high degree of compliance with standard SQL:
Precise calculations: For exact-value
numbers, calculations do not introduce floating-point errors. Instead, exact precision is used. For
example, MySQL treats a number such as .0001 as an exact value rather than
as an approximation, and summing it 10,000 times produces a result of exactly 1, not a value that is 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 library works.
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 server SQL mode.
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 5.7 handles numeric operations precisely. For information about controlling the SQL mode, see Section 5.1.7, "Server SQL Modes".