Count number of unique characters in a string

Question

I\'m looking for a sql statement to count the number of unique characters in a string.

e.g.

3333333333 -> returns 1
1113333333 -> returns 2
111         


        

Answer 1

DROP FUNCTION IF EXISTS test.count_chrs;
CREATE DEFINER=`test`@`localhost` FUNCTION `count_chrs`(s CHAR(100)) RETURNS CHAR(4)
  BEGIN 
    DECLARE string_length int(4);
    DECLARE unique_string CHAR(100) DEFAULT "";
    DECLARE count_unique int(4) DEFAULT 0;
    DECLARE current_char int(4) DEFAULT 1;
    SET string_length = CHAR_LENGTH(s);

    WHILE current_char <= string_length DO
      IF (!LOCATE(SUBSTR(s, current_char, 1), unique_string)) THEN
        SET count_unique = count_unique + 1;
        SET unique_string = CONCAT(unique_string, SUBSTR(s, current_char, 1));
      END IF;

      SET current_char = current_char + 1;
    END WHILE;

    RETURN count_unique; 
  END;

I'm very newbie with MySQL functions declaration, but this could turn you to the right way.