The CHAR_LENGTH function returns the number of characters in a character string. It is used to calculate the length of a CHAR, NCHAR, VARCHAR or VARNCHAR (and the synonym of such data type) string.
CHAR_LENGTH ( length_operand )
The following is an example that returns countries whose names consist of 15 - 16 characters from the nation table.
SELECT CHAR_LENGTH(name), name
WHERE CHAR_LENGTH(name) BETWEEN 15 AND 16
ORDER BY 1 ASC;
15 'Solomon Islands'
16 'Papua-New Guinea'