Home Database Mysql Tutorial sql varchar排序CAST/CONVERT实现语句

sql varchar排序CAST/CONVERT实现语句

Jun 07, 2016 pm 05:51 PM

文章介绍了在自己利用普通排序对数据进行排序时发现varchar字符串排序无法得到我们想要的结果,下面我们来介绍利用 case或convert来解决这个问题。

是今天在后台发现排序有问题。于是,没办法,改之。下面简单说一下MySQL的varchar排序问题,引以为戒。

示例表结构:
先来看一下,我的表结构

 代码如下 复制代码
show create table cardserver G
*************************** 1. row ***************************
       Table: cardserver
Create Table: CREATE TABLE `cardserver` (
  `id` int(11) NOT NULL default '0',
  `ver` int(11) default NULL,
  `createtime` datetime default NULL,
  `updatetime` datetime default NULL,
  `game_id` int(2) NOT NULL default '0',
  `server_id` varchar(2) NOT NULL default '',
  `server_name` varchar(40) NOT NULL default '',
  PRIMARY KEY  (`id`),
  UNIQUE KEY `game_id_server_id` (`game_id`,`server_id`),
  UNIQUE KEY `game_id_server_name` (`game_id`,`server_name`)
) ENGINE=InnoDB DEFAULT CHARSET=gbk

1 row in set (0.00 sec)因为有外键的存在,所以我不想改变字段类型,费劲啊。呵呵。虽然最后我还是选择了更改字段类型,这是后话。因为我本篇日志想要说明的是varchar排序问题。所以不再说明我是如何更改字段类型的,大家有兴趣可以搜索我以前的日志。(骗一下点击)
现象描述:
下面,我从里面以server_id排一下序,大家来看一下排序后的结果:

 代码如下 复制代码
select server_id from cardserver where game_id = 1 order by server_id desc limit 10;
+-----------+
| server_id |
+-----------+
| 8         |
| 7         |
| 6         |
| 5         |
| 4         |
| 3         |
| 2         |
| 10        |
| 1         |

+-----------+很明显,我想要的结果应该是 10,8,7,6,5 这样的。但是这个10排在了2的后面。按照字符串来排的。其实我是想把它当做数值来排。
手动转换类型:
用下面的方法就可以了,使server_id+0之后再排序,问题解决了。

 代码如下 复制代码
select server_id from cardserver where game_id = 1 order by server_id+0 desc limit 10;
+-----------+
| server_id |
+-----------+
| 10        |
| 8         |
| 7         |
| 6         |
| 5         |
| 4         |
| 3         |
| 2         |
| 1         |
+-----------+

使用MySQL函数CAST/CONVERT:
mysql为我们提供了两个类型转换函数:CAST和CONVERT,现成的东西我们怎能放过?
CAST() 和CONVERT() 函数可用来获取一个类型的值,并产生另一个类型的值。
这个类型 可以是以下值其中的 一个:
BINARY[(N)]
CHAR[(N)]
DATE
DATETIME
DECIMAL
SIGNED [INTEGER]
TIME
UNSIGNED [INTEGER]
所以我们也可以用CAST解决问题:

 代码如下 复制代码
select server_id from cardserver where game_id = 1 order by CAST(server_id as SIGNED) desc limit 10;
+-----------+
| server_id |
+-----------+
| 10        |
| 8         |
| 7         |
| 6         |
| 5         |
| 4         |
| 3         |
| 2         |
| 1         |
+-----------+

也可以使用CONVERT来搞定此问题:

 代码如下 复制代码
select server_id from cardserver where game_id = 1 order by CONVERT(server_id,SIGNED) desc limit 10;
+-----------+
| server_id |
+-----------+
| 10        |
| 8         |
| 7         |
| 6         |
| 5         |
| 4         |
| 3         |
| 2         |
| 1         |
+-----------+

总结:方法有很多要看自己动脑子了,所谓的条条大道通罗马也是这个意思了。

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

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

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)

Hot Topics

Java Tutorial
1657
14
PHP Tutorial
1257
29
C# Tutorial
1229
24
When might a full table scan be faster than using an index in MySQL? When might a full table scan be faster than using an index in MySQL? Apr 09, 2025 am 12:05 AM

Full table scanning may be faster in MySQL than using indexes. Specific cases include: 1) the data volume is small; 2) when the query returns a large amount of data; 3) when the index column is not highly selective; 4) when the complex query. By analyzing query plans, optimizing indexes, avoiding over-index and regularly maintaining tables, you can make the best choices in practical applications.

Can I install mysql on Windows 7 Can I install mysql on Windows 7 Apr 08, 2025 pm 03:21 PM

Yes, MySQL can be installed on Windows 7, and although Microsoft has stopped supporting Windows 7, MySQL is still compatible with it. However, the following points should be noted during the installation process: Download the MySQL installer for Windows. Select the appropriate version of MySQL (community or enterprise). Select the appropriate installation directory and character set during the installation process. Set the root user password and keep it properly. Connect to the database for testing. Note the compatibility and security issues on Windows 7, and it is recommended to upgrade to a supported operating system.

MySQL: Simple Concepts for Easy Learning MySQL: Simple Concepts for Easy Learning Apr 10, 2025 am 09:29 AM

MySQL is an open source relational database management system. 1) Create database and tables: Use the CREATEDATABASE and CREATETABLE commands. 2) Basic operations: INSERT, UPDATE, DELETE and SELECT. 3) Advanced operations: JOIN, subquery and transaction processing. 4) Debugging skills: Check syntax, data type and permissions. 5) Optimization suggestions: Use indexes, avoid SELECT* and use transactions.

Can mysql and mariadb coexist Can mysql and mariadb coexist Apr 08, 2025 pm 02:27 PM

MySQL and MariaDB can coexist, but need to be configured with caution. The key is to allocate different port numbers and data directories to each database, and adjust parameters such as memory allocation and cache size. Connection pooling, application configuration, and version differences also need to be considered and need to be carefully tested and planned to avoid pitfalls. Running two databases simultaneously can cause performance problems in situations where resources are limited.

RDS MySQL integration with Redshift zero ETL RDS MySQL integration with Redshift zero ETL Apr 08, 2025 pm 07:06 PM

Data Integration Simplification: AmazonRDSMySQL and Redshift's zero ETL integration Efficient data integration is at the heart of a data-driven organization. Traditional ETL (extract, convert, load) processes are complex and time-consuming, especially when integrating databases (such as AmazonRDSMySQL) with data warehouses (such as Redshift). However, AWS provides zero ETL integration solutions that have completely changed this situation, providing a simplified, near-real-time solution for data migration from RDSMySQL to Redshift. This article will dive into RDSMySQL zero ETL integration with Redshift, explaining how it works and the advantages it brings to data engineers and developers.

The relationship between mysql user and database The relationship between mysql user and database Apr 08, 2025 pm 07:15 PM

In MySQL database, the relationship between the user and the database is defined by permissions and tables. The user has a username and password to access the database. Permissions are granted through the GRANT command, while the table is created by the CREATE TABLE command. To establish a relationship between a user and a database, you need to create a database, create a user, and then grant permissions.

Laravel Eloquent ORM in Bangla partial model search) Laravel Eloquent ORM in Bangla partial model search) Apr 08, 2025 pm 02:06 PM

LaravelEloquent Model Retrieval: Easily obtaining database data EloquentORM provides a concise and easy-to-understand way to operate the database. This article will introduce various Eloquent model search techniques in detail to help you obtain data from the database efficiently. 1. Get all records. Use the all() method to get all records in the database table: useApp\Models\Post;$posts=Post::all(); This will return a collection. You can access data using foreach loop or other collection methods: foreach($postsas$post){echo$post->

MySQL: The Ease of Data Management for Beginners MySQL: The Ease of Data Management for Beginners Apr 09, 2025 am 12:07 AM

MySQL is suitable for beginners because it is simple to install, powerful and easy to manage data. 1. Simple installation and configuration, suitable for a variety of operating systems. 2. Support basic operations such as creating databases and tables, inserting, querying, updating and deleting data. 3. Provide advanced functions such as JOIN operations and subqueries. 4. Performance can be improved through indexing, query optimization and table partitioning. 5. Support backup, recovery and security measures to ensure data security and consistency.

See all articles