Table of Contents
回复内容:
Home Backend Development PHP Tutorial 涉及到金额的为什么都要保存整数?

涉及到金额的为什么都要保存整数?

Jun 06, 2016 pm 08:33 PM
java php thinkphp

比如金额是100.02,那么数据库中都要求存为10002

回复内容:

比如金额是100.02,那么数据库中都要求存为10002

希望对你有帮助:

  • 代码之谜(四)- 浮点数(从惊讶到思考)
  • 代码之谜(五)- 浮点数(谁偷了你的精度?)

浮点型计算不精确

为什么要用整形? 用 decimal 字段类型 不行吗? 如果涉及到计算,为了尽量保持最大的精确度,可以使用PHP 的中的 BC 数学 函数。注意,目前,浮点数在计算机中应该是无法完全精确存储的,只能最大限度。除非,你从数据库读取或从外部如GET参数获取的浮点数。

在实际的项目中,如果商品价格等 涉及到加减乘除运算时,也会按照一定约定一些规则进行取舍。 比如采用:四舍五入、向上递增、银行家舍入等等。

整数准确,速度又快。。。

浮点数不精确,计算会出现偏差

浮点数的精度:
http://php.net/manual/zh/language.types.float.php
以十进制能够精确表示的有理数如0.1或0.7,无论有多少尾数都不能被内部所使用的二进制精确表示.
因此不能在不丢失一点点精度的情况下转换为二进制的格式.
这就会造成混乱的结果,例如 floor((0.1+0.7)*10) 通常会返回 7 而不是预期中的 8.
因为该结果内部的表示其实是类似 7.9999999999999991118...
永远不要相信浮点数结果精确到了最后一位,也永远不要比较两个浮点数是否相等.
如果确实需要更高的精度,应该使用bcmath(Binary Calculator Math)函数或者gmp(GNU Multiple Precision)函数.
http://php.net/manual/zh/ref.bc.php
http://php.net/manual/zh/ref.gmp.php

为了保险起见,我们应该使用字符串来保存大整数,并且采用比如bcmath这样的数学函数库来进行计算.
比如用PHP对账户余额进行计算时,可以使用bcmath系列任意精度数学计算函数.
加 bcadd
减 bcsub
乘 bcmul
除 bcdiv
乘方 bcpow
开平方根 bcsqrt
比较 bccomp
取模(求余数) bcmod

<code><?php var_dump((0.5+0.2+0.3)==1); // bool(true)
var_dump((0.5+0.2+0.2+0.1)==1); // bool(false)
echo bccomp('1.01', '1', 1); // 保留1位小数,此时1.01等于1.返回0,表示两个数相等.
echo bccomp('1.01', '1', 2); // 保留2位小数,此时1.01大于1.返回1,表示左边的数比右边大.
</code></code>
Copy after login

浮点数存在精度的问题,数据库字段采用float和double型都容易产生误差.
如果存储对精度要求比较高的数据,比如账户余额,就不能使用float型了,这时应该使用decimal型.
比如我们将MySQL数据库字段"账户余额"的数据类型定义为decimal(5,2),这样就可以存放-999.99到999.99范围内的数,并且不会出现误差.括号里左边的数表示总有效位数,右边的数表示小数位数.如果范围不够用,可以定义为decimal(10,2).

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
2 weeks ago By 尊渡假赌尊渡假赌尊渡假赌
Repo: How To Revive Teammates
4 weeks ago By 尊渡假赌尊渡假赌尊渡假赌
Hello Kitty Island Adventure: How To Get Giant Seeds
4 weeks ago By 尊渡假赌尊渡假赌尊渡假赌

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

PHP 8.4 Installation and Upgrade guide for Ubuntu and Debian PHP 8.4 Installation and Upgrade guide for Ubuntu and Debian Dec 24, 2024 pm 04:42 PM

PHP 8.4 brings several new features, security improvements, and performance improvements with healthy amounts of feature deprecations and removals. This guide explains how to install PHP 8.4 or upgrade to PHP 8.4 on Ubuntu, Debian, or their derivati

How To Set Up Visual Studio Code (VS Code) for PHP Development How To Set Up Visual Studio Code (VS Code) for PHP Development Dec 20, 2024 am 11:31 AM

Visual Studio Code, also known as VS Code, is a free source code editor — or integrated development environment (IDE) — available for all major operating systems. With a large collection of extensions for many programming languages, VS Code can be c

How do you parse and process HTML/XML in PHP? How do you parse and process HTML/XML in PHP? Feb 07, 2025 am 11:57 AM

This tutorial demonstrates how to efficiently process XML documents using PHP. XML (eXtensible Markup Language) is a versatile text-based markup language designed for both human readability and machine parsing. It's commonly used for data storage an

Break or return from Java 8 stream forEach? Break or return from Java 8 stream forEach? Feb 07, 2025 pm 12:09 PM

Java 8 introduces the Stream API, providing a powerful and expressive way to process data collections. However, a common question when using Stream is: How to break or return from a forEach operation? Traditional loops allow for early interruption or return, but Stream's forEach method does not directly support this method. This article will explain the reasons and explore alternative methods for implementing premature termination in Stream processing systems. Further reading: Java Stream API improvements Understand Stream forEach The forEach method is a terminal operation that performs one operation on each element in the Stream. Its design intention is

PHP Program to Count Vowels in a String PHP Program to Count Vowels in a String Feb 07, 2025 pm 12:12 PM

A string is a sequence of characters, including letters, numbers, and symbols. This tutorial will learn how to calculate the number of vowels in a given string in PHP using different methods. The vowels in English are a, e, i, o, u, and they can be uppercase or lowercase. What is a vowel? Vowels are alphabetic characters that represent a specific pronunciation. There are five vowels in English, including uppercase and lowercase: a, e, i, o, u Example 1 Input: String = "Tutorialspoint" Output: 6 explain The vowels in the string "Tutorialspoint" are u, o, i, a, o, i. There are 6 yuan in total

Java Made Simple: A Beginner's Guide to Programming Power Java Made Simple: A Beginner's Guide to Programming Power Oct 11, 2024 pm 06:30 PM

Java Made Simple: A Beginner's Guide to Programming Power Introduction Java is a powerful programming language used in everything from mobile applications to enterprise-level systems. For beginners, Java's syntax is simple and easy to understand, making it an ideal choice for learning programming. Basic Syntax Java uses a class-based object-oriented programming paradigm. Classes are templates that organize related data and behavior together. Here is a simple Java class example: publicclassPerson{privateStringname;privateintage;

Create the Future: Java Programming for Absolute Beginners Create the Future: Java Programming for Absolute Beginners Oct 13, 2024 pm 01:32 PM

Java is a popular programming language that can be learned by both beginners and experienced developers. This tutorial starts with basic concepts and progresses through advanced topics. After installing the Java Development Kit, you can practice programming by creating a simple "Hello, World!" program. After you understand the code, use the command prompt to compile and run the program, and "Hello, World!" will be output on the console. Learning Java starts your programming journey, and as your mastery deepens, you can create more complex applications.

Java Program to Find the Volume of Capsule Java Program to Find the Volume of Capsule Feb 07, 2025 am 11:37 AM

Capsules are three-dimensional geometric figures, composed of a cylinder and a hemisphere at both ends. The volume of the capsule can be calculated by adding the volume of the cylinder and the volume of the hemisphere at both ends. This tutorial will discuss how to calculate the volume of a given capsule in Java using different methods. Capsule volume formula The formula for capsule volume is as follows: Capsule volume = Cylindrical volume Volume Two hemisphere volume in, r: The radius of the hemisphere. h: The height of the cylinder (excluding the hemisphere). Example 1 enter Radius = 5 units Height = 10 units Output Volume = 1570.8 cubic units explain Calculate volume using formula: Volume = π × r2 × h (4

See all articles