Syntax:
CHAR_LENGTH(str)

Returns the length of the string str, measured in code points. A
multibyte character counts as a single code point. This means that, for
a string containing two 3-byte characters, LENGTH() returns 6, whereas
CHAR_LENGTH() returns 2, as shown here:

mysql> SET @dolphin:='海豚';
Query OK, 0 rows affected (0.01 sec)

mysql> SELECT LENGTH(@dolphin), CHAR_LENGTH(@dolphin);
+------------------+-----------------------+
| LENGTH(@dolphin) | CHAR_LENGTH(@dolphin) |
+------------------+-----------------------+
|                6 |                     2 |
+------------------+-----------------------+
1 row in set (0.00 sec)

CHAR_LENGTH() returns NULL if str is NULL.

URL: https://dev.mysql.com/doc/refman/8.0/en/string-functions.html

