SPARQL/UNION

Suppose the set A: 28 capitals in European Union Template:SPARQL

Suppose the set B: 3 cities with millions of inhabitants in European Union. Template:SPARQL

The intersection of A and B, big capitals of the European Union, can simply be achieved by combining all the triples. This results in 1 city. Template:SPARQL

All capitals of the European union, excluding big cities can be achieved by filtering using FILTER NOT EXISTS { }. This results in the other 27 capitals. Template:SPARQL

Finally a UNION of capitals and big cities result in 30 cities, one of which was deduplicated by DISTINCT. Template:SPARQL Mind that the 2 parts of the union should both be within brackets { ... } UNION { ... }.

Two simpler examples of UNION are

• {?a wdt:P27 wd:Q55. } UNION { ?a wdt:P27 wd:Q29999. } Template:P for Template:Q or Template:Q.
• {?child wdt:P22 ?parent. } UNION {?child wdt:P25 ?parent. } Template:P or Template:P.

The last code can be simplified by using property path ?child wdt:P22|wdt:P25 ?parent.

An overview of all kind of joins:

Venn diagram	Mathematical		SPARQL
	$A\cap B$	And	A. B.
	$A\setminus B$		A. FILTER NOT EXISTS{ B. }
	$A$		A. OPTIONAL{ B. }
	$A\cup B$	Or	{ A. } UNION { B. }