MySQL-length()与char_length() [英] MySQL - length() vs char_length()

问题描述

length()和char_length()之间的主要区别是什么?

What's the main difference between length() and char_length()?

我相信它与二进制和非二进制字符串有关.是否有实际的理由将字符串存储为二进制?

I believe it has something to do with binary and non-binary strings. Is there any practical reason to store strings as binary?

mysql> select length('MySQL'), char_length('MySQL');
+-----------------+----------------------+
| length('MySQL') | char_length('MySQL') |
+-----------------+----------------------+
|               5 |                    5 |
+-----------------+----------------------+
1 row in set (0.01 sec)

推荐答案

LENGTH()返回字符串的长度(以字节为单位).
CHAR_LENGTH()返回以字符为单位的字符串的长度.

LENGTH() returns the length of the string measured in bytes.
CHAR_LENGTH() returns the length of the string measured in characters.

这与Unicode特别相关，在Unicode中，大多数字符都编码为两个字节.或UTF-8，其中字节数有所不同.例如:

This is especially relevant for Unicode, in which most characters are encoded in two bytes. Or UTF-8, where the number of bytes varies. For example:

select length(_utf8 '€'), char_length(_utf8 '€')
--> 3, 1

您可以看到，即使只有一个字符，欧元符号也占用3个字节(在UTF-8中被编码为0xE282AC).

As you can see the Euro sign occupies 3 bytes (it's encoded as 0xE282AC in UTF-8) even though it's only one character.

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