SAMPLE - SPARQLqueries

Understanding SAMPLE

SAMPLE is an aggregate function that returns one arbitrary value from a group. Unlike MIN or MAX which have deterministic behavior, SAMPLE can return any value. It's particularly useful when:

You need just one example from a group
All values in the group are effectively equivalent
You want to avoid GROUP BY errors without listing all variables

The specific value returned by SAMPLE may vary between query executions.

Basic SAMPLE Examples

One City per Country

Run ↗

SELECT ?country ?countryLabel (SAMPLE(?cityLabel) AS ?exampleCity) (COUNT(?city) AS ?cityCount)
WHERE {
  ?city wdt:P31 wd:Q515 ;
        wdt:P17 ?country .
  SERVICE wikibase:label { bd:serviceParam wikibase:language "en". ?city rdfs:label ?cityLabel. ?country rdfs:label ?countryLabel. }
}
GROUP BY ?country ?countryLabel
ORDER BY DESC(?cityCount)
LIMIT 15

Aggregate One example city plus total city count per country

This query counts all cities in each country and shows one example city name. SAMPLE picks any city from the group — the specific city may change between runs.

Example Work per Author

Run ↗

SELECT ?author ?authorLabel (SAMPLE(?workLabel) AS ?exampleWork) (COUNT(?work) AS ?workCount)
WHERE {
  ?work wdt:P50 ?author .
  ?author wdt:P31 wd:Q5 .
  SERVICE wikibase:label { bd:serviceParam wikibase:language "en". ?work rdfs:label ?workLabel. ?author rdfs:label ?authorLabel. }
}
GROUP BY ?author ?authorLabel
HAVING (COUNT(?work) > 50)
ORDER BY DESC(?workCount)
LIMIT 20

Aggregate Prolific authors with one example work

Find authors with many works and show one example. SAMPLE provides a representative work without needing to choose the first, longest, or most recent one.

SAMPLE vs Other Approaches

Avoiding Non-Aggregated Variable Errors

Run ↗

SELECT ?continent ?continentLabel (COUNT(?country) AS ?countryCount)
  (SAMPLE(?countryLabel) AS ?exampleCountry)
  (SUM(?population) AS ?totalPop)
WHERE {
  ?country wdt:P31 wd:Q6256 ;
           wdt:P30 ?continent ;
           wdt:P1082 ?population .
  SERVICE wikibase:label { bd:serviceParam wikibase:language "en". ?country rdfs:label ?countryLabel. ?continent rdfs:label ?continentLabel. }
}
GROUP BY ?continent ?continentLabel

Aggregate Continent stats with one example country

Without SAMPLE, including ?countryLabel would require adding it to GROUP BY, which would create one row per country instead of per continent. SAMPLE lets you include a representative value without changing the grouping.

SAMPLE with Images

Countries with Example Image

Run ↗

SELECT ?continent ?continentLabel (COUNT(?country) AS ?countryCount)
  (SAMPLE(?image) AS ?exampleImage)
WHERE {
  ?country wdt:P31 wd:Q6256 ;
           wdt:P30 ?continent ;
           wdt:P18 ?image .
  SERVICE wikibase:label { bd:serviceParam wikibase:language "en". }
}
GROUP BY ?continent ?continentLabel

Aggregate One representative image per continent

SAMPLE is particularly useful with images — you often just need one representative image rather than all of them. This query picks one country's image per continent.

Key Entities Used in Examples

Entity	Description
`wd:Q5`	Human
`wd:Q515`	City
`wd:Q6256`	Country
`wdt:P17`	Country
`wdt:P18`	Image
`wdt:P30`	Continent
`wdt:P31`	Instance of (type)
`wdt:P50`	Author
`wdt:P1082`	Population