Show ambassadors in order of the most numbers of postings, using XQuery

principals-and-chiefs-most-postings.xq

xquery version "3.0";

for $ambassador in collection('/db/cms/apps/principals-chiefs/data')/person
let $postings := $ambassador/role
let $how-many-postings := count($postings)
group by $how-many-postings
order by $how-many-postings descending
return
    <group postings="{$how-many-postings}" people-in-this-group="{count($ambassador)}">
        {
        for $a in $ambassador 
        return $a
        }
    </group>

principals-and-chiefs-most-postings_result-excerpt.xml

<group postings="16" people-in-this-group="1">
    <person id="jackson-john-brinkerhoff">
        <persName>
            <surname>Jackson</surname>
            <forename>John Brinkerhoff</forename>
            <altname>John B. Jackson</altname>
        </persName>
        <birth>1862</birth>
        <death>1920</death>
        <career>Non-career appointee</career>
        <residence location="nj"/>
        <role class="chief"  type="envoy-extraordinary-minister-plenipotentiary"  location="cl">
            <event type="appointed"  when="1902-10-13"/>
            <note>Declined appointment. Commissioned during a recess of the Senate.</note>
        </role>
        <role class="chief"  type="envoy-extraordinary-minister-plenipotentiary"  location="gr">
            <event type="appointed"  when="1902-10-13"/>
            <event type="credentialed"  when="1902-12-24"/>
            <event type="missionterminated">Recommissioned to serve concurrently as Diplomatic Agent
                in Bulgaria</event>
            <note>Commissioned during a recess of the Senate; recommissioned as Envoy Extraordinary
                and Minister Plenipotentiary to Greece, Romania, and Serbia after confirmation on
                Dec 8, 1902; resident at Athens. Also accredited to Romania and Serbia; resident at
                Athens.</note>
        </role>
        <role class="chief"  type="envoy-extraordinary-minister-plenipotentiary"  location="ro">
            <event type="appointed"  when="1902-10-13"/>
            <event type="credentialed"  when="1903-04-07"/>
            <event type="missionterminated">Recommissioned to a different combination of countries</event>
            <note>Commissioned during a recess of the Senate; recommissioned after confirmation on
                Dec 8, 1902. Commissioned to Greece, Romania, and Serbia; resident at Athens.</note>
        </role>
        <role class="chief"  type="envoy-extraordinary-minister-plenipotentiary"  location="xi">
            <event type="appointed"  when="1902-10-13"/>
            <note>Commissioned during a recess of the Senate; recommissioned after confirmation on
                Dec 8, 1902. Commissioned Envoy Extraordinary and Minister Plenipotentiary to
                Greece, Romania, and Serbia; took oath of office, but did not present credentials in
                Serbia until 1904; resident at Athens. Commissioned Jul 5, 1903, as Envoy
                Extraordinary and Minister Plenipotentiary to Greece, Romania, and Serbia and
                Diplomatic Agent in Bulgaria; resident at Athens.</note>
        </role>
        <role class="chief"  type="diplomatic-agent"  location="bg">
            <event type="appointed"  when="1903-06-05"/>
            <event type="credentialed"  when="1903-09-19"/>
            <event type="missionterminated">Recommissioned to a different combination of countries</event>
            <note>Commissioned as Envoy Extraordinary and Minister Plenipotentiary to Greece,
                Romania, and Serbia and Diplomatic Agent in Bulgaria; resident at Athens.
                Commissioned during a recess of the Senate; recommissioned after confirmation on Nov
                16, 1903.</note>
        </role>
        <role class="chief"  type="envoy-extraordinary-minister-plenipotentiary"  location="gr">
            <event type="appointed"  when="1903-06-05"/>
            <event type="missionterminated">Recommissioned to a different combination of countries</event>
            <note>Commissioned during a recess of the Senate; recommissioned as Envoy Extraordinary
                and Minister Plenipotentiary to Greece, Romania, and Serbia, and Diplomatic Agent in
                Bulgaria. Recommissioned after confirmation on Nov 16, 1903; resident at
                Athens.</note>
        </role>
        <role class="chief"  type="diplomatic-agent"  location="ro">
            <event type="appointed"  when="1903-06-05"/>
            <event type="missionterminated"  when="1905-07-25">Presented recall</event>
            <note>Commissioned as Envoy Extraordinary and Minister Plenipotentiary to Greece,
                Romania, and Serbia and Diplomatic Agent to Bulgaria; resident at Athens.
                Commissioned during a recess of the Senate; recommissioned after confirmation on Nov
                16, 1903.</note>
        </role>
        <role class="chief"  type="envoy-extraordinary-minister-plenipotentiary"  location="xi">
            <event type="appointed"  when="1903-07-05"/>
            <event type="credentialed"  when="1904-05-09"/>
            <event type="missionterminated"  when="1905-07-13">Presented recall</event>
            <note>Commissioned during a recess of the Senate as Envoy Extraordinary and Minister
                Plenipotentiary to Greece, Romania, and Serbia and Diplomatic Agent in Bulgaria;
                resident at Athens. Recommissioned on Nov 16, 1903. Commissioned to Romania and
                Serbia; resident at Bucharest.</note>
        </role>
        <role class="chief"  type="diplomatic-agent"  location="bg">
            <event type="appointed"  when="1905-03-08"/>
            <event type="missionterminated"  when="1907-06-04">Presented recall</event>
            <note>Commissioned as Envoy Extraordinary and Minister Plenipotentiary to Greece and
                Montenegro and Diplomatic Agent in Bulgaria; resident at Athens.</note>
        </role>
        <role class="chief"  type="envoy-extraordinary-minister-plenipotentiary"  location="gr">
            <event type="appointed"  when="1905-03-08"/>
            <event type="missionterminated"  when="1907-10-19">Presented recall</event>
            <note>Commissioned as Envoy Extraordinary and Minister Plenipotentiary to Greece and
                Montenegro and Diplomatic Agent in Bulgaria; resident at Athens.</note>
        </role>
        <role class="chief"  type="envoy-extraordinary-minister-plenipotentiary"  location="me">
            <event type="appointed"  when="1905-03-08"/>
            <event type="credentialed"  when="1905-10-30"/>
            <event type="missionterminated"  when="1907-10-27">Presented recall</event>
            <note>Accredited also to Greece and Bulgaria; resident at Athens.</note>
        </role>
        <role class="chief"  type="envoy-extraordinary-minister-plenipotentiary"  location="ir">
            <event type="appointed"  when="1907-07-01"/>
            <event type="credentialed"  when="1907-12-12"/>
            <event type="missionterminated"  when="1909-07-03">Left post</event>
            <note>Commissioned during a recess of the Senate; recommissioned after confirmation on
                Dec 12, 1907. Commissioned to Persia.</note>
        </role>
        <role class="chief"  type="envoy-extraordinary-minister-plenipotentiary"  location="cu">
            <event type="appointed"  when="1909-12-21"/>
            <event type="credentialed"  when="1910-03-22"/>
            <event type="missionterminated"  when="1911-10-27">Presented recall</event>
        </role>
        <role class="chief"  type="envoy-extraordinary-minister-plenipotentiary"  location="bg">
            <event type="appointed"  when="1911-08-12"/>
            <event type="credentialed"  when="1912-02-01"/>
            <event type="missionterminated"  when="1913-10-18">Presented recall</event>
            <note>Commissioned as Envoy Extraordinary and Minister Plenipotentiary to Romania,
                Serbia, and Bulgaria; resident at Bucharest.</note>
        </role>
        <role class="chief"  type="envoy-extraordinary-minister-plenipotentiary"  location="ro">
            <event type="appointed"  when="1911-08-12"/>
            <event type="credentialed"  when="1911-12-24"/>
            <event type="missionterminated"  when="1913-10-28">Presented recall</event>
            <note>Commissioned as Envoy Extraordinary and Minister Plenipotentiary to Romania,
                Serbia, and Bulgaria; resident at Bucharest.</note>
        </role>
        <role class="chief"  type="envoy-extraordinary-minister-plenipotentiary"  location="xi">
            <event type="appointed"  when="1911-08-12"/>
            <event type="credentialed"  when="1912-01-16"/>
            <event type="missionterminated"  when="1913-10-15">Presented recall</event>
            <note>Commissioned as Envoy Extraordinary and Minister Plenipotentiary to Romania,
                Serbia, and Bulgaria; resident at Bucharest.</note>
        </role>
    </person>
</group>