MySQL - length() 与 char_length()

问题描述

length() 和 char_length() 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.将字符串存储为二进制有什么实际原因吗?

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() 返回以字节为单位的字符串长度.
CHAR_LENGTH() 返回以字符为单位的字符串长度.

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

这与 Unicode 尤其相关，其中大多数字符以两个字节进行编码.或 UTF-8，其中字节数不同.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

如您所见，欧元符号占用了 3 个字节(它在 UTF-8 中编码为 0xE282AC)，即使它只有一个字符.

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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