SELECT `idx`, `file_name`, `file_extension` FROM `board_file` WHERE `del_flag`='n' AND `board_data_idx`= and image_type='sub'

There is an error in the transmitted query.
ERROR_CODE 1064 : You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'and image_type='sub'' at line 1