how could select more than 14 column
You are hitting the limit on the GROUP_CONCAT() results length - group_concat_max_len as can be seen in http://sqlfiddle.com/#!9/bb7a66/16

You can raise it temporarily for your query:

SET SESSION group_concat_max_len = 10240;


http://sqlfiddle.com/#!9/bb7a66/19