MongoDB由两个字段求和？
要按两个字段求和，可以使用聚合框架。首先让我们创建一个包含文档的集合
> db.orderByTwoFieldsDemo.insertOne({"Value1":10,"Value2":35});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ca285576304881c5ce84baa")
}
> db.orderByTwoFieldsDemo.insertOne({"Value1":12,"Value2":5});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ca2855f6304881c5ce84bab")
}
> db.orderByTwoFieldsDemo.insertOne({"Value1":55,"Value2":65});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ca285686304881c5ce84bac")
}以下是在find()方法的帮助下显示集合中所有文档的查询
> db.orderByTwoFieldsDemo.find().pretty();
这将产生以下输出
{
"_id" : ObjectId("5ca285576304881c5ce84baa"),
"Value1" : 10,
"Value2" : 35
}
{
"_id" : ObjectId("5ca2855f6304881c5ce84bab"),
"Value1" : 12,
"Value2" : 5
}
{
"_id" : ObjectId("5ca285686304881c5ce84bac"),
"Value1" : 55,
"Value2" : 65
}情况1：以下是按两个字段求和排序的查询，并以升序获取结果：
> db.orderByTwoFieldsDemo.aggregate(
... [
... {$project:{Value1:1, Value2:1, orderBySumValue:{$add: ["$Value1", "$Value2"]}}},
... {$sort:{orderBySumValue:1}}]
... );这将产生以下输出
{ "_id" : ObjectId("5ca2855f6304881c5ce84bab"), "Value1" : 12, "Value2" : 5,
"orderBySumValue" : 17 }
{ "_id" : ObjectId("5ca285576304881c5ce84baa"), "Value1" : 10, "Value2" : 35,
"orderBySumValue" : 45 }
{ "_id" : ObjectId("5ca285686304881c5ce84bac"), "Value1" : 55, "Value2" : 65,
"orderBySumValue" : 120 }情况2：以下是按两个字段求和排序的查询，并按降序获得结果
> db.orderByTwoFieldsDemo.aggregate( [ {$project:{Value1:1, Value2:1,
orderBySumValue:{$add: ["$Value1", "$Value2"]}}}, {$sort:{orderBySumValue:-1}}] );这将产生以下输出
{ "_id" : ObjectId("5ca285686304881c5ce84bac"), "Value1" : 55, "Value2" : 65,
"orderBySumValue" : 120 }
{ "_id" : ObjectId("5ca285576304881c5ce84baa"), "Value1" : 10, "Value2" : 35,
"orderBySumValue" : 45 }
{ "_id" : ObjectId("5ca2855f6304881c5ce84bab"), "Value1" : 12, "Value2" : 5,
"orderBySumValue" : 17 }