Thanks a lot to Bob Vale!
I changed the function that he suggested a bit to indicate a custom separator.
UPDATE:
This feature is not perfect. It produces strangs results when the beginning or end of a line is the same as a separator, and when a line contains more than one separator per line, so you need to make sure that it is not the case in your lines.
CREATE FUNCTION `SPLIT_SORT`(inString TEXT, inSeparator TEXT) RETURNS text CHARSET utf8 BEGIN DECLARE strings INT DEFAULT 0; -- number of substrings DECLARE forward INT DEFAULT 1; -- index for traverse forward thru substrings DECLARE backward INT; -- index for traverse backward thru substrings, position in calc. substrings DECLARE remain TEXT; -- work area for calc. no of substrings -- swap areas TEXT for string compare, INT for numeric compare DECLARE swap1 TEXT; -- left substring to swap DECLARE swap2 TEXT; -- right substring to swap SET remain = inString; SET backward = LOCATE(inSeparator, remain); WHILE backward != 0 DO SET strings = strings + 1; SET backward = LOCATE(inSeparator, remain); SET remain = SUBSTRING(remain, backward+1); END WHILE; IF strings < 2 THEN RETURN inString; END IF; REPEAT SET backward = strings; REPEAT SET swap1 = SUBSTRING_INDEX(SUBSTRING_INDEX(inString,inSeparator,backward-1),inSeparator,-1); SET swap2 = SUBSTRING_INDEX(SUBSTRING_INDEX(inString,inSeparator,backward),inSeparator,-1); IF swap1 > swap2 THEN SET inString = TRIM(BOTH inSeparator FROM CONCAT_WS(inSeparator ,SUBSTRING_INDEX(inString,inSeparator,backward-2) ,swap2,swap1 ,SUBSTRING_INDEX(inString,inSeparator,(backward-strings)))); END IF; SET backward = backward - 1; UNTIL backward < 2 END REPEAT; SET forward = forward +1; UNTIL forward + 1 > strings END REPEAT; RETURN inString; END;