CHAR_LENGTH(str)

The string str length measured in characters is returned by CHAR_LENGTH. It also counts a single character for a multibyte character. This means, for a string containing five 2-byte characters, LENGTH() returns 10, whereas CHAR_LENGTH() returns 5.

CHARACTER_LENGTH(str)

CHARACTER_LENGTH() is a synonym for CHAR_LENGTH().

mysql> SELECT CHAR_LENGTH('hello');
+----------------------+
| CHAR_LENGTH('hello') |
+----------------------+
|                    5 |
+----------------------+
1 row in set (0.00 sec)

mysql> SELECT CHAR_LENGTH('23569874');
+-------------------------+
| CHAR_LENGTH('23569874') |
+-------------------------+
|                       8 |
+-------------------------+
1 row in set (0.00 sec)