Follow Techotopia on Twitter

On-line Guides
All Guides
eBook Store
iOS / Android
Linux for Beginners
Office Productivity
Linux Installation
Linux Security
Linux Utilities
Linux Virtualization
Linux Kernel
System/Network Admin
Programming
Scripting Languages
Development Tools
Web Development
GUI Toolkits/Desktop
Databases
Mail Systems
openSolaris
Eclipse Documentation
Techotopia.com
Virtuatopia.com

How To Guides
Virtualization
General System Admin
Linux Security
Linux Filesystems
Web Servers
Graphics & Desktop
PC Hardware
Windows
Problem Solutions

  




 

 

Chapter 24. Precision Math

MySQL 5.1 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 1, 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 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 sql_mode system variable.

An important result of these features is that MySQL 5.1 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 5.1 handles numeric operations precisely. For information about using the sql_mode system variable to control the SQL mode, see Section 5.2.5, “The Server SQL Mode”.


 
 
  Published under the terms of the GNU General Public License Design by Interspire