Correct the issue with multiple csv import

I have a code, that can upload all csv files into database. and pick the lowest price. After i upgraded to php7 and use mariaDB . it dosnt work anymore. it need to change connection type to mariadb instead of mysqli so here is the task 1. Change db connection to mariaDB 2. Check if there is issue in calculation with prices comparision (It works, but just to be more safe)