Efficiency of conventional thermal power production for district heating

PREFIX owl: <http://www.w3.org/2002/07/owl#>
PREFIX sdmx-measure: <http://purl.org/linked-data/sdmx/2009/measure#> 
PREFIX sdmx-dimension: <http://purl.org/linked-data/sdmx/2009/dimension#> 
PREFIX property: <http://rdfdata.eionet.europa.eu/eurostat/property#> 
PREFIX indic_nrg: <http://dd.eionet.europa.eu/vocabulary/eurostat/indic_nrg/>
PREFIX unit: <http://dd.eionet.europa.eu/vocabulary/eurostat/unit/>
PREFIX geo: <http://dd.eionet.europa.eu/vocabulary/eurostat/geo/>
PREFIX product: <http://dd.eionet.europa.eu/vocabulary/eurostat/product/>
PREFIX sdmx-attribute: <http://purl.org/linked-data/sdmx/2009/attribute#> 

SELECT
bif:either (?ugeo = 'DE', 'Germany', ?country) as ?ugeo
round((sum(xsd:double(?last_year))-sum(xsd:double(?first_year)))*10)/10.0 as ?delta
sum(xsd:double(?first_year)) as ?first_year
sum(xsd:double(?last_year)) as ?last_year

{{
SELECT
?country
?ugeo
bif:either(?year = 2005, sum(?efficiency_rate),0) AS ?first_year
bif:either(?year = 2016, sum(?efficiency_rate),0) AS ?last_year
{{
SELECT DISTINCT
    ?country
    ?ugeo
    year(?date) as ?year
    #sum(?nrg_100a_B_101109)
    #sum(?nrg_100a_B_101009)
    round((sum(xsd:double(?nrg_100a_B_101109)) / sum(xsd:double(?nrg_100a_B_101009)))*1000)/10.0 as ?efficiency_rate
  WHERE {{
    GRAPH <http://rdfdata.eionet.europa.eu/eurostat/data/nrg_100a.rdf.gz> { 
    {    
    _:nrg_100a sdmx-dimension:timePeriod ?date .
    _:nrg_100a sdmx-dimension:refArea ?geo .
    _:nrg_100a sdmx-attribute:unitMeasure unit:KTOE .
    _:nrg_100a property:product product:0000 .

    {
      _:nrg_100a property:indic_nrg indic_nrg:B_101109 . 
      _:nrg_100a sdmx-measure:obsValue ?nrg_100a_B_101109 .
    } UNION {
      
      _:nrg_100a property:indic_nrg indic_nrg:B_101009 . 
     _:nrg_100a sdmx-measure:obsValue ?nrg_100a_B_101009 .
    }
 }} ?geo skos:notation ?ugeo .
    ?geo skos:prefLabel ?country .
}}
GROUP BY ?country ?date ?ugeo
HAVING sum(?nrg_100a_B_101009) > 0
}}
}} 
ORDER BY desc(?delta) ?country ?date