与多个字段不同，并与mongodb中的条件

Question

我想编写一个相当于distinct和where 的查询。 SQL查询是select DISTINCT key,score from GPC where note="test2" and notetwo = "meet2"

{ "_id" : ObjectId("4dc86fef6a0aa8513ab5f21c"), "key" : "SAGAR","score" : 16, "note" : "test1", "notetwo" : "meet1" } 
{ "_id" : ObjectId("4dc86ffd6a0aa8513ab5f21d"), "key" : "SAGAR456", "score" : 17, "note" : "testjh1", "notetwo" : "meetjh1" } 
{ "_id" : ObjectId("4dc8700b6a0aa8513ab5f21e"), "key" : "SAGAR33", "score" : 37, "note" : "test2", "notetwo" : "meet2" } 
{ "_id" : ObjectId("4dc871686a0aa8513ab5f21f"), "key" : "SAGAR33", "score" : 37, "note" : "test2", "notetwo" : "meet2" } 
{ "_id" : ObjectId("4dc871696a0aa8513ab5f220"), "key" : "SAGAR33", "score" : 37, "note" : "test2", "notetwo" : "meet2" } 
{ "_id" : ObjectId("4dc8716c6a0aa8513ab5f221"), "key" : "SAGAR456", "score" : 17, "note" : "testjh1", "notetwo" : "meetjh1" } 

从查询

预期结果是

[{ “键”： “SAGAR33”， “得分”：37}]

什么是等效查询mongodb。我正在使用猫鼬来执行查询。

Answer 1

您将需要使用aggregate查询来实现此目的。下面是将在外壳的工作（其可以被转化为容易猫鼬）的示例：

db.gpc.aggregate([ 
    // your where clause: note="test2" and notetwo = "meet2" 
    {"$match" : {note:"test2", notetwo:"meet2"}}, 
    // group by key, score to get distinct 
    {"$group" : {_id : {key:"$key", score:"$score"}}}, 
    // Clean up the output 
    {"$project" : {_id:0, key:"$_id.key", score:"$_id.score"}} 
]) 

输出：

{ "result" : [ { "key" : "SAGAR33", "score" : 37 } ], "ok" : 1 }