Approaching database design
I don't know about mysql/mariadb, but a postgresql DB allows you to store arrays.  An array of 86400 sensorValues would allow you to have one record per entry_id, dim_id,  dim_date.

create table sensorvalues (
  entry_id serial primary key,
  dim_id int,
  dim_date date,
  sensorvalue int[86400]
);