Improve SPARQL for the time range - sparql

Question

I am trying to make some sparql query statement with python programming and I got stuck below. What I am trying to make is query statement of the time range somehow general manner. Give me an example below. Question is "Who was the mayor of the new york city in %(YEAR)?" and corresponding sparql I write is same as below. For the far previous range, it works okay. But the recent range, it doesn't work because the current mayor does not have end time. In other words, can I make a code something like FIlTER (?v3 has no value or ?v3 > "2011-01-01"^^xsd:dateTime) ? I'd like to improve my sparql with one query in more general manner corresponding to the time range questions.
CASE 1: Who was the mayor of the new york city in 2011? -ok
SELECT DISTINCT ?v ?vLabel ?v2 ?v3
WHERE
{
wd:Q60 p:P6 ?stmt.
?stmt ps:P6 ?v;
pq:P580 ?v2;
pq:P582 ?v3.
FILTER (?v2 < "2011-01-01"^^xsd:dateTime) # start time
FILTER (?v3 > "2011-01-01"^^xsd:dateTime) # end time
SERVICE wikibase:label { bd:serviceParam wikibase:language "ko,en". }
}
ORDER BY DESC (?v2)
CASE 2: Who was the mayor of the new york city in 2016? - No answer
SELECT DISTINCT ?v ?vLabel ?v2 ?v3
WHERE
{
wd:Q60 p:P6 ?stmt.
?stmt ps:P6 ?v;
pq:P580 ?v2;
pq:P582 ?v3
FILTER (?v2 < "2016-01-01"^^xsd:dateTime) # start time
FILTER (?v3 > "2016-01-01"^^xsd:dateTime) # end time
SERVICE wikibase:label { bd:serviceParam wikibase:language "ko,en". }
}
ORDER BY DESC (?v2)

Answer 1

Step 1: Get the query pattern to match even if there is no value for “end time”. This can be done using OPTIONAL for that triple pattern:
OPTIONAL { ?stmt pq:P582 ?v3 }
Step 2: Change the filter so that it accepts solutions where the end time variable ?v3 has no value. This can be done using the bound function, which returns true if there is a value and false otherwise:
FILTER (!bound(?v3) || ?v3 > "2016-01-01"^^xsd:dateTime) # end time
Complete query:
SELECT DISTINCT ?v ?vLabel ?v2 ?v3
WHERE
{
wd:Q60 p:P6 ?stmt.
?stmt ps:P6 ?v;
pq:P580 ?v2.
OPTIONAL { ?stmt pq:P582 ?v3 }
FILTER (?v2 < "2016-01-01"^^xsd:dateTime) # start time
FILTER (!bound(?v3) || ?v3 > "2016-01-01"^^xsd:dateTime) # end time
SERVICE wikibase:label { bd:serviceParam wikibase:language "ko,en". }
}
ORDER BY DESC (?v2)