CouchDB视图为每个“组”返回一个元素

async function view_reduce() {
  let result = await db.query('SO-66173759/most_recent', {
    reduce: true,
    group_level: 1,
    descending: true
  });
  // show  
  gel('view_reduce').innerText = result.rows.map(row => `${row.key}\t${row.value}`).join('\n');

  return result;
}

async function showMostRecentDocs() {
  // Use results from reduce to get documents
  let result = await view_reduce();
  // The result row values are document ids; use allDocs to fetch the docs 
  result = await db.allDocs({
    include_docs: true,
    keys: result.rows.map(row => row.value)
  });
  //show  
  gel('view_most_recent').innerText = result.rows.map(row => [row.doc.CompanyId, row.doc.Date, row.doc.Author].join('\t')).join('\n');
}

async function showViewKeyValues() {
  let result = await db.query('SO-66173759/most_recent', {
    reduce: false,
    include_docs: false
  });
  //show  
  gel('view_key_value').innerText =
    result.rows.map(row => `[${row.key}]\t${row.value}`).join('\n');
}

async function showViewDocs() {
  let result = await db.query('SO-66173759/most_recent', {
    reduce: false,
    include_docs: true
  });
  //show  
  gel('view_docs').innerText = result.rows.map(row => [row.doc.CompanyId, row.doc.Date, row.doc.Author].join('\t')).join('\n');
}

function getDocsToInstall(count) {
  const sourceDocs = [{
      "CompanyId": "Acme Amalgamated",
      "Author": "Wile E. Coyote",
    },
    {
      "CompanyId": "Acme Amalgamated",
      "Author": "Road R. Unner",
    },
    {
      "CompanyId": "Lorem Ipsum Inc.",
      "Author": "Caesar Augustus",
    },
    {
      "CompanyId": "Lorem Ipsum Inc.",
      "Author": "Marcus Aurelius",
    },
    {
      "CompanyId": "Cyberdyne Systems",
      "Author": "Miles Dyson",
    }
  ];
  // design document
  const ddoc = {
    "_id": "_design/SO-66173759",
    "views": {
      "most_recent": {
        "map": `function (doc) {             
           if(doc.CompanyId && doc.Date) {                         
              emit([doc.CompanyId,doc.Date],doc._id);
           }
        }`,
        "reduce": `function(keys,values,rereduce) {               
           return values[0];
        }`
      }
    }
  };

  // create a set of random documents.
  let docs = new Array(count);
  const dateSeed = [new Date(2010, 0, 1), new Date(), 0, 24];
  while (count--) {
    let doc = Object.assign({}, sourceDocs[Math.random() * sourceDocs.length | 0]);
    doc.Date = randomDate(...dateSeed).toISOString();
    docs[count] = doc;
  }
  docs.push(ddoc);
  return docs;
}

const db = new PouchDB('SO-66173759', {
  adapter: 'memory'
});
// install docs and show view in various forms.
(async() => {
  await db.bulkDocs(getDocsToInstall(20));
  await showViewDocs();
  await showViewKeyValues();
  return showMostRecentDocs();
})();

const gel = id => document.getElementById(id);

/*
https://stackoverflow.com/questions/31378526/generate-random-date-between-two-dates-and-times-in-javascript/31379050#31379050
*/
function randomDate(start, end, startHour, endHour) {
  var date = new Date(+start + Math.random() * (end - start));
  var hour = startHour + Math.random() * (endHour - startHour) | 0;
  date.setHours(hour);
  return date;
}

<script src="https://cdn.jsdelivr.net/npm/pouchdb@7.1.1/dist/pouchdb.min.js"></script>
<script src="https://github.com/pouchdb/pouchdb/releases/download/7.1.1/pouchdb.memory.min.js"></script>
<div>View: distinct, most recent</div>
<pre id='view_most_recent'></pre>
<hr/>
<div>View: reduce result</div>
<pre id='view_reduce'></pre>
<hr/>
<div>View: key/value</div>
<pre id='view_key_value'></pre>
<hr/>
<div>View: docs</div>
<pre id='view_docs'></pre>