CouchDB，如何在一个视图中计算两个值

Question

我有这样的文件：

{"user": "A","year": "2016","price": 3,"litres": 19900}
{"user": "B","year": "2016","price": 2.3,"litres": 16000}
{"user": "C","year": "2016","price": 2.9,"litres": 15000}
{"user": "A","year": "2015","price": 4,"litres": 12030}
{"user": "B","year": "2015","price": 3,"litres": 20002}
{"user": "C","year": "2015","price": 2.9,"litres": 22000}

我需要按年计算所有值的总和以及其中一个用户的总和，目标是将全球平均值与一个用户进行比较。

例如，如果我使用 "A" 调用视图作为求和升的键，我需要在减少类似以下内容后得到：

["A","2016"] {global: 50900, user: 19900}
["A","2015"] {global: 54032, user: 12030}

谢谢，

迭戈

Answer 1

您无法通过一次通话完成此操作。如果您交换键顺序，那么年份是第一位的，然后是用户，您可以对具有不同组级别的同一视图进行两次调用。组级别 1 将为您提供全球年份总数，组级别 2 将为您提供按用户总数划分的年份。

Answer 2

嗯..这是我的想法：

可以使用POST设置两个Key

function(doc) {
  var total={};
  total={year:doc.year,litres:doc.litres};
  emit(doc.user, {user:total,years:[total]});
  emit("", {user:"",years:[total]});
}

查询：

     curl -X POST  http://localhost:5984/test_a/_design/test/_view/test -H "Content-type:application/json" -d '{"keys":["A",""]}'

结果（缩短）：

 "key":"A","value":{"user":{"year":"2016","litres":19900},"years":    [{"year":"2016","litres":19900}]}},
"key":"A","value":{"user":{"year":"2015","litres":12030},"years":[{"year":"2015","litres":12030}]}},
"key":"","value":{"user":"","years":[{"year":"2016","litres":19900}]}},
"key":"","value":{"user":"","years":[{"year":"2016","litres":16000}]}},
"key":"","value":{"user":"","years":[{"year":"2016","litres":15000}]}},
"key":"","value":{"user":"","years":[{"year":"2015","litres":12030}]}},
"key":"","value":{"user":"","years":[{"year":"2015","litres":20002}]}},
"key":"","value":{"user":"","years":[{"year":"2015","litres":22000}]}}

如果您然后进行从两个键收集数据的减少：

function(keys, values, rereduce) {
  var user_sum=0;
  var total_a=[];
  var v_values={};
  var curUser="";
  for (var i=0;i<keys.length;i++) {
    if (keys[i]!="") {
      curUser=keys[i][0];
    }
    values[i].years.forEach(function(year) {
      if (v_values["year_"+year.year]) {
        v_values["year_"+year.year]=
          {year:year.year,  
           litres:v_values["year_"+year.year].litres+year.litres
          };
      }else{
        v_values["year_"+year.year]={year:year.year,litres:year.litres};
      }
   });

 }
 return ({user:curUser,years:v_values})

}

你得到

{"rows":[
  {"key":"A","value":
    {"user":"A",
     "years":{
       "year_2015":   {"year":"2015","litres":12030},
       "year_2016":{"year":"2016","litres":19900}
     }
    }
  },
 {"key":"","value":
   {"user":"",
    "years":{
      "year_2015":{"year":"2015","litres":54032},
      "year_2016":{"year":"2016","litres":50900}
    }
   }
 }

] }

我有点懒..所以请自行检查减少/重新减少...

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