1 . export by shell 

a.sql

use dbname; SELECT id,iab_num  FROM iab_list ;

mysql   -h host -uusername -P3306 -ppassword   dbname     < a.sql  > iab.out

refer :

https://stackoverflow.com/questions/356578/how-to-output-mysql-query-results-in-csv-format

https://stackoverflow.com/questions/935556/mysql-dump-by-query

http://www.tech-recipes.com/rx/1475/save-mysql-query-results-into-a-text-or-csv-file/

mysql export query result