Character Sets and Comparison Rules

Introduction to Character Sets

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Function: In order to make the data "understandable" by both humans and computers.

We know that only binary data can be stored in a computer, so how to store strings? Of course, the mapping relationship between characters and binary data is established. To establish this relationship, at least two things need to be clarified:

1. Which characters are you mapping to binary data? That is to define a clear range of characters.
2. How to map? The process of mapping a character to a binary data is also called encoding, and the process of mapping a binary data to a character is called decoding. People abstract the concept of a character set to describe the encoding rules of a certain range of characters. For example, let's define a character set named xiaohaizi, which contains character ranges and encoding rules as follows: Contains characters 'a', 'b', 'A', 'B'. The encoding rules are as follows: One byte is used to encode one character, and the mapping relationship between characters and bytes is as follows: 'a' -> 00000001 (hexadecimal: 0x01) 'b' -> 00000010 (hexadecimal: 0x02) 'A' -> 00000011 (hexadecimal: 0x03) 'B' -> 00000100 (hexadecimal: 0x04) With the xiaohaizi character set, we can represent some strings in binary form, the following is Binary representation of some strings encoded in the xiaohaizi character set: 'bA' -> 0000001000000011 (hexadecimal: 0x0203) 'baB' -> 000000100000000100000100 (hexadecimal: 0x020104) 'cd' -> unrepresentable, character Set xiaohaizi does not contain characters 'c' and 'd'

——Quoting "How MySQL Works"

Introduction to Comparison Rules

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1. Convert two characters with different case to uppercase or lowercase.
2. Then compare the binary data corresponding to these two characters.

Note: The same character set can have multiple comparison rules

utf8 and utf8mb4 in MySQL

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utf8mb3: The castrated utf8 character set, which only uses 1 to 3 bytes to represent characters.

utf8mb4: The authentic utf8 character set, using 1 to 4 bytes to represent characters.

View mysql character set

SHOW (CHARACTER SET|CHARSET) [LIKE 匹配的模式];

Check mysql comparison rules

SHOW COLLATION [LIKE 匹配的模式];

Note: Each character set corresponds to several comparison rules, and each character set has a default comparison rule

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