[Wikidata-bugs] [Maniphest] [Created] T152773: COUNT with GROUP BY timing out if used as sub query

[hoo]

hoo created this task. hoo added a project: Wikidata-Query-Service. Herald added a subscriber: Aklapper. Herald added projects: Wikidata, Discovery.

TASK DESCRIPTION

SELECT ?pred WHERE {
  {
    SELECT ?pred (COUNT(?value) AS ?bar) WHERE
    {
      ?subj ?pred ?value .
    } GROUP BY ?pred ORDER BY DESC(?bar) LIMIT 1000
  }
}

times out, while

SELECT ?pred (COUNT(?value) AS ?bar) WHERE
{
  ?subj ?pred ?value .
} GROUP BY ?pred ORDER BY DESC(?bar) LIMIT 1000

doesn't.

Disabling the optimizer doesn't help here.

Potentially related https://jira.blazegraph.com/browse/BLZG-1252, although not flattening the sub query is what's desired here.

It works if re-written using named sub-queries:

SELECT ?prop ?bar WITH {
    SELECT ?pred (COUNT(?value) AS ?bar) WHERE
    {
      ?subj ?pred ?value .
    } GROUP BY ?pred ORDER BY DESC(?bar) LIMIT 1000
  } AS %inner
  WHERE {
    INCLUDE %inner
} ORDER BY DESC(?bar)

TASK DETAIL

https://phabricator.wikimedia.org/T152773

EMAIL PREFERENCES

https://phabricator.wikimedia.org/settings/panel/emailpreferences/

To: hoo
Cc: Jonas, Smalyshev, Aklapper, hoo, EBjune, mschwarzer, Avner, debt, Gehel, D3r1ck01, FloNight, Xmlizer, Izno, jkroll, Wikidata-bugs, Jdouglas, aude, Deskana, Manybubbles, Mbch331

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