SELECT YEAR(a.datestmp) 'Vuosi',
       SUM(IF(a.category='Capital',a.eur,0)) 'Pääoma',
       SUM(IF(a.category='Fuel',a.eur,0)) 'Polttoaine',
       SUM(IF(a.category='Insurance',a.eur,0)) 'Vakuutus',
       SUM(IF(a.category='Maintenance',a.eur,0)) 'Huolto',
       SUM(IF(a.category='Other',a.eur,0)) 'Muut',
       SUM(a.eur) 'Yhteensä',
       b.kmMax-b.kmMin 'Kilometrit',
       SUM(eur)/(b.kmMax-b.kmMin) 'EUR/km'
       FROM costs AS a
         LEFT JOIN
         ( SELECT YEAR(bb.datestmp) 'Vuosi', MIN(bb.km) 'kmMin', MAX(bb.km) 'kmMax' FROM costs AS bb WHERE bb.datestmp<=DATE(NOW()) AND km>0 GROUP BY YEAR(bb.datestmp) ) AS b
       ON
         YEAR(a.datestmp)=b.Vuosi
       WHERE
         a.datestmp<=DATE(NOW())
       GROUP BY YEAR(a.datestmp);

+-------+----------+------------+----------+--------+--------+-----------+------------+----------+
| Vuosi | Pääoma   | Polttoaine | Vakuutus | Huolto | Muut   | Yhteensä  | Kilometrit | EUR/km   |
+-------+----------+------------+----------+--------+--------+-----------+------------+----------+
|  2016 |  8426.05 |    1229.41 |   397.34 | 199.00 | 178.77 |  10430.57 |      14568 | 0.715992 |
|  2017 |  3427.32 |    1699.80 |   395.43 | 257.00 | 196.85 |   5976.40 |      19234 | 0.310721 |
|  2018 |  3427.32 |    1117.47 |   703.92 | 359.35 | 119.40 |   5727.46 |      11634 | 0.492304 |
|  2019 |  3427.32 |       0.00 |     0.00 |   0.00 |   0.00 |   3427.32 |       NULL |     NULL |
|  2020 |  3427.32 |       0.00 |     0.00 |   0.00 |   0.00 |   3427.32 |       NULL |     NULL |
+-------+----------+------------+----------+--------+--------+-----------+------------+----------+

SELECT datestmp,
       km,
       eur,
       liter,
       eur/liter 'EUR/l',
       km-(SELECT km FROM costs AS b WHERE b.km < a.km AND category='Fuel' ORDER BY km DESC LIMIT 1) 'km/tank', 
       liter/((km-(SELECT km FROM costs AS b WHERE b.km < a.km AND category='Fuel' ORDER BY km DESC LIMIT 1))/100) 'l/100km' 
FROM costs AS a 
WHERE category='Fuel' 
ORDER BY km ASC;

+------------+-------+-------+-------+----------+---------+----------+
| datestmp   | km    | eur   | liter | EUR/l    | km/tank | l/100km  |
+------------+-------+-------+-------+----------+---------+----------+
| 2016-01-07 |    48 | 48.58 | 36.28 | 1.339030 |    NULL |     NULL |
| 2016-01-10 |   358 | 25.55 | 19.30 | 1.323834 |     310 | 6.225806 |
| 2016-01-10 |   619 | 20.06 | 14.98 | 1.339119 |     261 | 5.739464 |
| 2016-01-16 |  1141 | 40.59 | 31.25 | 1.298880 |     522 | 5.986590 |
| 2016-01-19 |  1563 | 33.00 | 25.60 | 1.289063 |     422 | 6.066351 |
| 2016-01-29 |  2110 | 42.69 | 32.61 | 1.309108 |     547 | 5.961609 |
| 2016-02-18 |  2610 | 41.60 | 32.27 | 1.289123 |     500 | 6.454000 |
| 2016-03-10 |  2961 | 32.00 | 24.35 | 1.314168 |     351 | 6.937322 |
| 2016-03-14 |  3749 | 52.19 | 40.18 | 1.298905 |     788 | 5.098985 |
| 2016-03-28 |  4496 | 49.61 | 38.34 | 1.293949 |     747 | 5.132530 |
| 2016-04-01 |  5016 | 40.98 | 31.55 | 1.298891 |     520 | 6.067308 |
| 2016-04-23 |  5582 | 51.60 | 39.12 | 1.319018 |     566 | 6.911661 |
| 2016-05-20 |  6111 | 48.46 | 35.66 | 1.358946 |     529 | 6.741021 |
| 2016-05-24 |  6450 | 25.81 | 18.65 | 1.383914 |     339 | 5.501475 |
| 2016-06-07 |  6659 | 17.62 | 12.66 | 1.391785 |     209 | 6.057416 |
| 2016-06-09 |  7033 | 38.91 | 27.23 | 1.428939 |     374 | 7.280749 |
| 2016-06-24 |  7454 | 32.03 | 23.23 | 1.378820 |     421 | 5.517815 |
| 2016-06-29 |  7827 | 28.31 | 20.38 | 1.389107 |     373 | 5.463807 |
| 2016-07-08 |  8334 | 38.96 | 28.67 | 1.358912 |     507 | 5.654832 |
| 2016-07-09 |  8815 | 36.65 | 27.37 | 1.339057 |     481 | 5.690229 |
| 2016-07-13 |  9204 | 31.61 | 22.76 | 1.388840 |     389 | 5.850900 |
| 2016-07-20 |  9667 | 34.97 | 26.51 | 1.319125 |     463 | 5.725702 |
| 2016-08-22 | 10309 | 52.03 | 39.45 | 1.318885 |     642 | 6.144860 |
| 2016-08-29 | 10590 | 20.70 | 15.69 | 1.319312 |     281 | 5.583630 |
| 2016-09-23 | 11111 | 55.01 | 40.18 | 1.369089 |     521 | 7.712092 |
| 2016-10-12 | 11712 | 56.50 | 40.10 | 1.408978 |     601 | 6.672213 |
| 2016-10-30 | 12342 | 52.27 | 37.10 | 1.408895 |     630 | 5.888889 |
| 2016-11-04 | 12901 | 42.20 | 30.60 | 1.379085 |     559 | 5.474061 |
| 2016-11-12 | 13240 | 26.79 | 20.16 | 1.328869 |     339 | 5.946903 |
| 2016-12-05 | 13865 | 54.70 | 39.67 | 1.378876 |     625 | 6.347200 |
| 2016-12-27 | 14569 | 57.43 | 41.05 | 1.399026 |     704 | 5.830966 |
| 2017-01-13 | 15150 | 54.47 | 38.12 | 1.428909 |     581 | 6.561102 |
| 2017-01-23 | 15789 | 56.51 | 39.27 | 1.439012 |     639 | 6.145540 |
| 2017-01-27 | 16040 | 23.14 | 16.54 | 1.399033 |     251 | 6.589641 |
| 2017-02-25 | 16585 | 56.14 | 37.70 | 1.489125 |     545 | 6.917431 |
| 2017-03-23 | 17175 | 55.44 | 38.26 | 1.449033 |     590 | 6.484746 |
| 2017-04-06 | 17741 | 48.18 | 32.36 | 1.488875 |     566 | 5.717314 |
| 2017-04-29 | 18410 | 56.25 | 38.82 | 1.448995 |     669 | 5.802691 |
| 2017-05-09 | 18702 | 26.38 | 18.59 | 1.419042 |     292 | 6.366438 |
| 2017-05-28 | 19204 | 49.00 | 32.47 | 1.509085 |     502 | 6.468127 |
| 2017-06-21 | 19788 | 48.03 | 33.38 | 1.438886 |     584 | 5.715753 |
| 2017-06-27 | 20579 | 62.37 | 43.34 | 1.439086 |     791 | 5.479140 |
| 2017-06-29 | 21229 | 52.60 | 34.63 | 1.518914 |     650 | 5.327692 |
| 2017-07-01 | 21703 | 35.34 | 24.39 | 1.448954 |     474 | 5.145570 |
| 2017-07-03 | 22117 | 31.23 | 21.55 | 1.449188 |     414 | 5.205314 |
| 2017-07-09 | 22729 | 48.92 | 33.76 | 1.449052 |     612 | 5.516340 |
| 2017-07-11 | 23196 | 37.85 | 26.49 | 1.428841 |     467 | 5.672377 |
| 2017-07-14 | 23894 | 55.20 | 37.32 | 1.479100 |     698 | 5.346705 |
| 2017-07-21 | 24638 | 52.70 | 37.27 | 1.414006 |     744 | 5.009409 |
| 2017-08-01 | 25306 | 56.59 | 41.04 | 1.378899 |     668 | 6.143713 |
| 2017-08-13 | 25885 | 50.12 | 36.08 | 1.389135 |     579 | 6.231434 |
| 2017-08-19 | 26534 | 57.12 | 37.85 | 1.509115 |     649 | 5.832049 |
| 2017-09-01 | 27194 | 53.74 | 38.47 | 1.396933 |     660 | 5.828788 |
| 2017-09-02 | 27683 | 39.40 | 26.82 | 1.469053 |     489 | 5.484663 |
| 2017-09-02 | 27978 | 25.53 | 17.50 | 1.458857 |     295 | 5.932203 |
| 2017-09-06 | 28303 | 31.30 | 21.02 | 1.489058 |     325 | 6.467692 |
| 2017-09-06 | 28568 | 18.79 | 12.88 | 1.458851 |     265 | 4.860377 |
| 2017-09-10 | 28805 | 22.02 | 14.99 | 1.468979 |     237 | 6.324895 |
| 2017-09-13 | 29154 | 31.19 | 20.81 | 1.498799 |     349 | 5.962751 |
| 2017-09-13 | 29732 | 46.99 | 31.35 | 1.498884 |     578 | 5.423875 |
| 2017-09-15 | 30055 | 28.30 | 18.88 | 1.498941 |     323 | 5.845201 |
| 2017-09-16 | 30773 | 62.24 | 41.52 | 1.499037 |     718 | 5.782730 |
| 2017-09-24 | 31356 | 50.90 | 34.23 | 1.487000 |     583 | 5.871355 |
| 2017-09-30 | 31685 | 29.32 | 21.42 | 1.368814 |     329 | 6.510638 |
| 2017-10-08 | 32172 | 41.74 | 29.21 | 1.428963 |     487 | 5.997947 |
| 2017-10-21 | 32759 | 55.75 | 40.87 | 1.364081 |     587 | 6.962521 |
| 2017-11-07 | 33358 | 54.71 | 38.83 | 1.408962 |     599 | 6.482471 |
| 2017-12-11 | 33988 | 58.10 | 39.28 | 1.479124 |     630 | 6.234921 |
| 2017-12-25 | 34384 | 36.20 | 26.06 | 1.389102 |     396 | 6.580808 |
| 2018-01-23 | 34916 | 47.68 | 33.96 | 1.404005 |     532 | 6.383459 |
| 2018-02-21 | 35259 | 43.05 | 30.23 | 1.424082 |     343 | 8.813411 |
| 2018-03-30 | 35679 | 44.93 | 31.89 | 1.408906 |     420 | 7.592857 |
| 2018-04-14 | 36300 | 51.80 | 36.12 | 1.434109 |     621 | 5.816425 |
| 2018-04-27 | 36848 | 45.63 | 31.93 | 1.429064 |     548 | 5.826642 |
| 2018-05-02 | 37539 | 64.67 | 42.02 | 1.539029 |     691 | 6.081042 |
| 2018-05-06 | 38234 | 54.77 | 37.03 | 1.479071 |     695 | 5.328058 |
| 2018-06-01 | 38873 | 63.24 | 39.55 | 1.598989 |     639 | 6.189358 |
| 2018-06-04 | 39384 | 43.84 | 28.67 | 1.529125 |     511 | 5.610568 |
| 2018-06-06 | 40015 | 63.97 | 40.51 | 1.579116 |     631 | 6.419968 |
| 2018-06-09 | 40524 | 45.93 | 29.65 | 1.549073 |     509 | 5.825147 |
| 2018-06-15 | 41122 | 50.51 | 32.19 | 1.569121 |     598 | 5.382943 |
| 2018-06-16 | 41591 | 39.46 | 26.15 | 1.508987 |     469 | 5.575693 |
| 2018-06-23 | 42186 | 52.46 | 34.42 | 1.524114 |     595 | 5.784874 |
| 2018-06-29 | 42533 | 28.98 | 19.73 | 1.468829 |     347 | 5.685879 |
| 2018-07-12 | 43115 | 52.09 | 34.29 | 1.519102 |     582 | 5.891753 |
| 2018-07-17 | 43451 | 30.39 | 20.34 | 1.494100 |     336 | 6.053571 |
| 2018-07-26 | 43949 | 53.75 | 34.26 | 1.568885 |     498 | 6.879518 |
| 2018-09-14 | 44645 | 67.51 | 41.96 | 1.608913 |     696 | 6.028736 |
| 2018-10-17 | 45176 | 52.41 | 35.32 | 1.483862 |     531 | 6.651601 |
| 2018-11-04 | 45639 | 44.00 | 29.75 | 1.478992 |     463 | 6.425486 |
| 2018-11-17 | 46153 | 46.56 | 30.45 | 1.529064 |     514 | 5.924125 |
| 2018-11-25 | 46475 | 29.84 | 20.88 | 1.429119 |     322 | 6.484472 |
+------------+-------+-------+-------+----------+---------+----------+