Detailed explanation of character sets and collation rules in MySQL

MySQL is a widely used relational database management system. In order to support character sets and collation rules between different languages ​​and cultures, MySQL provides a variety of character set and collation settings.

Character set and collation are very important concepts in MySQL and play a vital role in the data storage and query process. Let's take a closer look at the character sets and collation rules in MySQL.

1. Character set

The character set in MySQL determines how data is stored in the database. Common character sets include ASCII, UTF-8, GB2312, etc. Commonly used character sets and their meanings are as follows:

1. ASCII

ASCII is a 7-bit character encoding standard used to represent English characters, numbers and basic symbols, applicable Common character encodings in English systems. The ASCII-encoded character set has 128 characters, including control characters such as line feeds and tabs.

2. UTF-8

UTF-8 is a universal code that can represent all characters in the world, including Chinese characters and other non-Latin alphabet characters. It uses variable length encoding, and the encoding length of each character is different, generally using 1 to 4 bytes. UTF-8 encoding follows the Unicode standard and is a modern character encoding method that has become a widely used character set on the Internet.

3. GB2312

GB2312 is a Chinese character set that can represent Chinese characters, English and numbers. It was formulated by the National Standardization Administration Committee in 1980. The character set of GB2312 includes a standard character library composed of 3755 simplified Chinese characters and 682 non-Chinese characters.

The above are common character sets. MySQL also supports other character sets, such as Latin1, GBK, etc. When creating a database or table, you need to specify the character set used, for example:

CREATE DATABASE test_database CHARACTER SET utf8;

2. Sorting rules

The sorting rules determine the data Sorting methods, common sorting rules include ASCII, UTF-8, GB2312, etc.

1. The relationship between character sets and collation rules

The character sets and collation rules in MySQL are related to each other. For example, when using the Chinese character set, you need to select the corresponding Sort the order correctly.

Collation rules have some common suffixes:

_ci: case insensitive, that is, it is not case-sensitive. Uppercase and lowercase letters will be treated as the same characters when sorting.

_cs: Case sensitive, that is, it is case-sensitive. Uppercase and lowercase letters will be treated as different characters when sorting.

_bin: Use binary sorting, that is, directly compare binary values. For example, the comparison results of 0x41 and 0x61 are different.

For example, in the UTF-8 character set, when using the utf8_general_ci collation rule, for the upper and lower case letters a and A, they are regarded as equal when sorting, which is the effect of case insensitivity.

2. Commonly used collation rules

There are many collation rules to choose from in MySQL. Here are some commonly used collation rules:

2.1 utf8_general_ci

This is a commonly used sorting rule that can ignore case and merge and sort characters such as diacritics. For example, á, à, â and a will be considered equal when sorting.

2.2 utf8_bin

This is a binary sorting rule that distinguishes differences in characters such as uppercase and lowercase, diacritics, etc., and performs complete binary sorting for special characters.

2.3 utf8_unicode_ci

This sorting rule can sort characters and numbers at the same time, and can sort data containing different character sets.

2.4 gb2312_chinese_ci

This is a sorting rule for Chinese character sets. When sorting Chinese characters, English, numbers and other characters, ensure that Chinese characters are sorted in the order of Chinese pinyin.

3. Application scenarios of character sets and collation rules

In actual development, it is necessary to select the appropriate character set and collation rules according to the actual situation. Generally speaking, the following situations require special attention:

1. Multi-language data storage and query: it is necessary to use character sets and collation rules that support multiple languages, such as UTF-8 character set and utf8_unicode_ci sorting rule.
2. Sort special characters: For data containing special characters such as diacritics, appropriate sorting rules are generally used for sorting.
3. Chinese data sorting: For Chinese data, you need to use character sets and collation rules that support Chinese, such as GB2312 character set and gb2312_chinese_ci collation rule.
4. Sensitive data query: For situations where sensitive data query is required, it is recommended to use case-sensitive sorting rules.

Summary:

The character set and collation rules in MySQL are a very important concept in the database and play a vital role in the data storage and query process. In actual development, it is necessary to select the appropriate character set and sorting rules according to the actual situation to ensure the correct saving and querying of data.

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