How to output only English labels in SPARQL query?

Question

I don't understand why this SPARQL queries produce duplicates:

SELECT DISTINCT ?WikidataItem ?itemLabel
WHERE {  
  ?WikidataItem rdfs:label ?itemLabel. 
  ?WikidataItem ?label "Mozilla Firefox"@en.  
}
LIMIT 5

Try it here.

Is it producing a row of output in every language? How can I change my query in order for it to produce only the single result in English?

Update

I'm still confused about how to solve my problem, since I perhaps oversimplified my example. I actually am using FILTER(CONTAINS(LCASE(?itemLabel), "firefox"@en)) among other things to limit my query. How do I output only the English language label for each entry?

Answer 1

Is it producing a row of output in every language?

Yes, you're correct: ?itemLabel match labels in all languages.

Try simply SELECT * {?item rdfs:label "Mozilla Firefox"@en}.

If you want to project a variable, use VALUES:

SELECT * {VALUES (?label) {("Mozilla Firefox"@en)} ?item rdfs:label ?label}