tb_factory表由 factory_code 和 factory_name 字段，查询出如下所示效果：

{"factory_0001": "工厂1","factory_0002": "工厂2",...
}

select sql：

SELECT CONCAT( "{",GROUP_CONCAT( CONCAT( CONCAT( "\"",factory_code,"\"" ),":",CONCAT( "\"",factory_name,"\"" )) SEPARATOR ',' ),"}") AS factory_codes
FROM tb_factory