MySQL 中的 CHAR_LENGTH() 或 CHARACTER_LENGTH() 字符串函数用于检索指定字符串的长度。该函数只会计算字符数，而忽略字符是单字节还是多字节。
mysql> Select CHAR_LENGTH('New Delhi');
+--------------------------+
| CHAR_LENGTH('New Delhi') |
+--------------------------+
| 9 |
+--------------------------+
1 row in set (0.00 sec)
mysql> Select CHAR_LENGTH('NewDelhi');
+-------------------------+
| CHAR_LENGTH('NewDelhi') |
+-------------------------+
| 8 |
+-------------------------+
1 row in set (0.00 sec)
mysql> Select CHARACTER_LENGTH('NewDelhi');
+------------------------------+
| CHARACTER_LENGTH('NewDelhi') |
+------------------------------+
| 8 |
+------------------------------+
1 row in set (0.00 sec)
mysql> Select CHARACTER_LENGTH('New Delhi');
+-------------------------------+
| CHARACTER_LENGTH('New Delhi') |
+-------------------------------+
| 9 |
+-------------------------------+
1 row in set (0.00 sec)
