数据库主键设计原则
数据库主键设计原则 或许大家都设计过数据库,也为表定义过主键,今天我想阐述的是,应该如何正确的设计一个主键,在以往的一些资料中,都没有提及到主键设计的原则.我为此总结了一下: 1.是否要采用GUID作为主键 用GUID作主键有它的优势与不足.优势是GUID具有唯一
数据库主键设计原则或许大家都设计过数据库,也为表定义过主键,今天我想阐述的是,应该如何正确的设计一个主键,在以往的一些资料中,都没有提及到主键设计的原则.我为此总结了一下:
1.是否要采用GUID作为主键
用GUID作主键有它的优势与不足.优势是GUID具有唯一性,在任何情况下,可以产生全球唯一的值.这是GUID最大的优势,也方便数据导入,比如要求从另一个系统中把数据导入进来,那么,不用担心,导入时,会导致主键冲突.不足是GUID值太复杂.不易记忆,因为有时,难免我们会用记录的方式,来进行记录判断.而且数据太长,影响数据库效率.GUID的产生不是以一定的次序产生,对于按主键物理排序的数据库来说,如果在记录的前部插入一条记录,可能会导致后面N次方的数据条数后移.这将导致数据插入效率.因此GUID的采用应该要慎重.
2.是否要采用自动递增的方式
对于以前谈到的主键,要求唯一性,因此大家都用自动递增的方式.这样的方式是非常不可取的.可能是为了方便插入记录时,不必去人为创建主键值.以为这样会方便,其实不是的.带来的麻烦要远远胜于这种所谓的"方便".第一:数据导入不方便,经常会有从另一系统导入数据进来,自动递增的主键,将不允许原表中的ID被导入进来.这会导致主键丢失.第二:对于象订单这样的有主外键的表来说,如果订单的"主档表"主键是自动生成的.那么在保存一个订单时,会要求对主档表与明细表同进行事务保存,而此时,先要生成一条订单,然后取出这个订单自动生成的主键,然后再把此作为明细表的一个外键,进行明细的保存.这过程中,将变以复杂而且不可行.事务如何处理.订单主档表插入记录后,要是明细保存时遇到错误,主档表记录还要进行删除.烦.插入成功以后,还要取出产生的最大值.这将是一个严重的浪费.记录多的话会影响速度,而且会存在并行插入.导致获取的记录可能是不正确的. 因此在以上的严重问题下,请不要采用自动递增方式.
3.是否要采用int型作为主键
以前大家都采用int型，都是出来主键都是数字导致的．其实我们也明白．并不是只是数字的东西就是数字型的．比如电话号码等．因此对于主键，采用int型的优势是速度快，插入，查询时都可能会比其他的方式快．但我这种快的效果也未必有多明显，比如以varchar(15)为例，物理主键排序的数据，会自动以主键进行物理数据排序．因此，就算是字符型的数据，在插入时也会插入到相应的物理位置上，也就是说，在插入时可能会影响一些速度．但在以后的查询中，速度影响不会太明显．而我要说的，不采用int型作为主键，不是说，里面不存数据．我还是建议大家在主键中存放数字，这样的排序比较要比夹杂字母的排序来的快，之所以要采用字符型，也是为以后的数据导入作准备，有一天，会要求从其他表导入数据时，可以在导入数据的主键上加一个特定字母来避免与原主键冲突．比如在导入数据的主键前加一个＂Ｎ＂字母．这也就不用担心，要求导入数据表中的主键是数字型还是字符型了．
４．是否采用编号来定义主键
这个问题是老生常谈了．主键设计有个原则，就是主键不应具有任何实际意义．这条其实是非常重要，有人就是觉得编号本身是唯一的，可以作为主键用，但可能会为以后带来麻烦．因为带有实际意义的字段，还是存在被修改的可能性．而对于主键最大的忌讳就是修改主键，这可能会导致非常严重的不可估计的后果．比如学生编号，平时以为永远不会修改，但修改的可能还是会存在．
还有一种，表面上是唯一的，但实际上应该是允许重复的．我举个例子，订单吧，订单编号应该是唯一吧．是的．可是会存在这样的情况，一张原来的订单是因为某个原因，要求订单作废．那好给订单的状态标识为＂cancel＂．然后允许再次录入同样编号的订单．因此．对于这样的情况下在，虽然有效的订单编号只有一个，但在数据库角度会允许编号重复．所以不管如何，还是建议大家为表都建一个没有任何意义的主键，如ＩＤ．
因此，总结一下，我在设计主键，会采用字符型的．不采用自动递增，在新增记录时，系统生成主键值．一般为全数字进行存入，至于主键值的生成规则，可以按需求进行规则定义．如果没有特殊的要求，只是为了保持唯一，可以定义一个字段存放一个数值．在生成时，自动加一．然后再存回去．这也比从一个表中寻找最大值要来的快吧．
好了．我一时就想起这么多．有建议的一起讨论．．
听棠
http://tintown.blogbus.com/
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
1392
52
Honor Magic V3 debuts AI defocus eye protection technology: effectively alleviates the development of myopia
Jul 18, 2024 am 09:27 AM
According to news on July 12, the Honor Magic V3 series was officially released today, equipped with the new Honor Vision Soothing Oasis eye protection screen. While the screen itself has high specifications and high quality, it also pioneered the introduction of AI active eye protection technology. It is reported that the traditional way to alleviate myopia is "myopia glasses". The power of myopia glasses is evenly distributed to ensure that the central area of sight is imaged on the retina, but the peripheral area is imaged behind the retina. The retina senses that the image is behind, promoting the eye axis direction. grow later, thereby deepening the degree. At present, one of the main ways to alleviate the development of myopia is the "defocus lens". The central area has a normal power, and the peripheral area is adjusted through optical design partitions, so that the image in the peripheral area falls in front of the retina.
iOS 18 adds a new 'Recovered' album function to retrieve lost or damaged photos
Jul 18, 2024 am 05:48 AM
Apple's latest releases of iOS18, iPadOS18 and macOS Sequoia systems have added an important feature to the Photos application, designed to help users easily recover photos and videos lost or damaged due to various reasons. The new feature introduces an album called "Recovered" in the Tools section of the Photos app that will automatically appear when a user has pictures or videos on their device that are not part of their photo library. The emergence of the "Recovered" album provides a solution for photos and videos lost due to database corruption, the camera application not saving to the photo library correctly, or a third-party application managing the photo library. Users only need a few simple steps
Vivo's phone with the strongest signal! vivo X100s is equipped with a universal signal amplification system: 21 antennas, 360° surround design
Jun 03, 2024 pm 08:41 PM
According to news on May 13, vivoX100s was officially released tonight. In addition to excellent images, the new phone also performs very well in terms of signal. According to vivo’s official introduction, vivoX100s uses an innovative universal signal amplification system, which is equipped with up to 21 antennas. This design has been re-optimized based on the direct screen to balance many signal requirements such as 5G, 4G, Wi-Fi, GPS, and NFC. This makes vivoX100s the mobile phone with the strongest signal reception capability in vivo’s history. The new phone also uses a unique 360° surround design, with antennas distributed around the body. This design not only enhances the signal strength, but also optimizes various daily holding postures to avoid problems caused by improper holding methods.
Honor X60i mobile phone is on sale starting from 1,399 yuan: visual quadrilateral OLED direct screen
Jul 29, 2024 pm 08:25 PM
According to news on July 29, the Honor X60i mobile phone is officially on sale today, starting at 1,399 yuan. In terms of design, the Honor X60i mobile phone adopts a straight screen design with a hole in the center and almost unbounded ultra-narrow borders on all four sides, which greatly broadens the field of view. Honor X60i parameters Display: 6.7-inch high-definition display Battery: 5000mAh large-capacity battery Processor: Dimensity 6080 processor (TSMC 6nm, 2x2.4G A76+6×2G A55) System: MagicOS8.0 system Other features: 5G signal enhancement, smart capsule, under-screen fingerprint, dual MIC, noise reduction, knowledge Q&A, photography capabilities: rear dual camera system: 50 million pixels main camera, 2 million pixels auxiliary lens, front selfie lens: 8 million pixels, price: 8GB
New stacking process! Xiaomi MIX Fold 4 is equipped with Jinshajiang 'three-dimensional special-shaped' battery for the first time
Jul 20, 2024 am 03:20 AM
According to news on July 19, Xiaomi MIX Fold 4, the first flagship folding new phone, was officially released tonight and is equipped with a "three-dimensional special-shaped battery" for the first time. According to reports, Xiaomi MIX Fold4 has achieved a major breakthrough in battery technology and designed an innovative "three-dimensional special-shaped battery" specifically for folding screens. Traditional folding screen devices mostly use conventional square batteries, which have low space utilization efficiency. In order to solve this problem, Xiaomi did not use the common winding battery cells, but developed a new lamination process to create a new form of battery, which greatly improved the space utilization. Battery Technology Innovation In order to accurately alternately stack positive and negative electrode sheets and ensure the safe embedding of lithium ions, Xiaomi has developed a new ultrasonic welding machine and lamination machine to improve welding and cutting accuracy.
Detailed tutorial on establishing a database connection using MySQLi in PHP
Jun 04, 2024 pm 01:42 PM
How to use MySQLi to establish a database connection in PHP: Include MySQLi extension (require_once) Create connection function (functionconnect_to_db) Call connection function ($conn=connect_to_db()) Execute query ($result=$conn->query()) Close connection ( $conn->close())
How to handle database connection errors in PHP
Jun 05, 2024 pm 02:16 PM
To handle database connection errors in PHP, you can use the following steps: Use mysqli_connect_errno() to obtain the error code. Use mysqli_connect_error() to get the error message. By capturing and logging these error messages, database connection issues can be easily identified and resolved, ensuring the smooth running of your application.
The 2024 Apple iPad Pro/Air does not support the second-generation Apple Pencil: you can buy a new one if you need it
May 08, 2024 pm 04:07 PM
According to news on May 8, Apple’s new iPad Pro/Air tablets have been released. According to Apple’s official website, the new iPad Pro and iPad Air no longer support the second-generation Apple Pencil released in 2018, but only support Apple Pencil Pro and Apple Pencil (USB- C). Apple Pencil (USB-C) will be released in November 2023. This stylus maintains the same pixel-level accuracy, low latency, and tilt-angle sensing features as the first and second-generation Apple Pencil, while eliminating pressure sensitivity. function and does not support wireless charging. Its price is 649 yuan. And the newly released ApplePe
