SPARQL get all the data before it reaches timeout

Question

I am trying to get all the city names of all countries in the world using this below query. Whenever I execute this below query it returns this message "Query timeout limit reached".

Is there any other way to get all the data before it reaches timeout limit?

SELECT ?country ?countryLabel ?city ?cityLabel
WHERE
{
  ?city wdt:P31/wdt:P279* wd:Q515;
        wdt:P17 ?country .

  SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en". }
}
ORDER BY ?country

Answer 1

Based on my comment, take out the ORDER BY.

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Why? It has probably to do with the query optimizer, but I don't have any real explanation. In general, with SQL that I'm more familiar, ORDER BY when unnecessary is the first thing to take out when improving query performance.

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(Note that this question was cross-posted at StackOverflow, and there is a longer discussion there.)