MySQL : strange LENGTH() behaviour on utf8 string

Question

我正在对请求生成器进行单元测试，但我遇到了 LENGTH 函数的问题。

我有 2 个请求:

SHOW VARIABLES LIKE '%character%'

返回以下结果:

array(8) {
  [0] =>
  array(2) {
    'Variable_name' =>
    string(20) "character_set_client"
    'Value' =>
    string(4) "utf8"
  }
  [1] =>
  array(2) {
    'Variable_name' =>
    string(24) "character_set_connection"
    'Value' =>
    string(4) "utf8"
  }
  [2] =>
  array(2) {
    'Variable_name' =>
    string(22) "character_set_database"
    'Value' =>
    string(6) "latin1"
  }
  [3] =>
  array(2) {
    'Variable_name' =>
    string(24) "character_set_filesystem"
    'Value' =>
    string(6) "binary"
  }
  [4] =>
  array(2) {
    'Variable_name' =>
    string(21) "character_set_results"
    'Value' =>
    string(4) "utf8"
  }
  [5] =>
  array(2) {
    'Variable_name' =>
    string(20) "character_set_server"
    'Value' =>
    string(4) "utf8"
  }
  [6] =>
  array(2) {
    'Variable_name' =>
    string(20) "character_set_system"
    'Value' =>
    string(4) "utf8"
  }
  [7] =>
  array(2) {
    'Variable_name' =>
    string(18) "character_sets_dir"
    'Value' =>
    string(26) "/usr/share/mysql/charsets/"
  }
}

我的第二个请求是:

SELECT LENGTH('重庆') as len

它返回 6 而不是 2。

这里有什么问题吗？我的字符集参数看起来不错。

Answer 1

我在 MySQL documentation 中找到了答案:

LENGTH 函数计算字节:

mysql> SELECT LENGTH('重庆') ;
+------------------+
| LENGTH('重庆')   |
+------------------+
|                6 |
+------------------+
1 row in set (0.00 sec)

CHAR_LENGTH 函数计算字符:

mysql> SELECT CHAR_LENGTH('重庆') ;
+-----------------------+
| CHAR_LENGTH('重庆')   |
+-----------------------+
|                     2 |
+-----------------------+
1 row in set (0.00 sec)