MongoDB中SQL中减集操作的等效操作是什么？答案

【问题标题】：what is the equivalent operation in MongoDB for Minus set operation in SQL?MongoDB中SQL中减集操作的等效操作是什么？
【发布时间】：2017-05-24 18:32:53
【问题描述】：

我有以下 MongoDB 集合：

feb = [{
    "_id" : ObjectId("591df31cbbcd51d52653553c"),
    "patientId" : 2,
    "fullName" : "Lopez , Julia",
    "EVOLUCIÓN" : "Medicada"
}, ...]



may = [
    {"_id" : ObjectId("59231f3ab36e83e3db6e03f8"),
    "patientId" : 4,
    "fullName" : "Martinez , Carolina",
    "EVOLUCIÓN" : "15/08/97 : MEDICADA CON DERRUMAL A TERMINAR, TOMANIL GEL, ADAXIL AMP, ZOCOR 5, RENITEC 5, CERVILANE, Y AMLOC 5."
}, ...]

我需要使用 MongoDB 查询获取 feb 的投影 - 可能超过 fullName。在 SQL 中是：

SELECT fullName
FROM feb
MINUS
SELECT fullName
FROM may;

【问题讨论】：

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标签： mysql sql mongodb

【解决方案1】：

您不能在MongoDB 中一次跨多个集合进行查询。您必须在应用程序级别使用两个单独的查询来模拟 MINUS：

首先，你会得到五月的名字：

namesInMay = db.may.distinct("fullName");

然后，您对二月执行相同操作，但使用 $nin 运算符过滤掉那些也在 namesInMay 中的：

db.feb.distinct("fullName", { "fullName": { $nin: namesInMay }});

【讨论】：

【解决方案2】：

试试这样的...

db.address.aggregate([
{
  $replaceRoot: { 
    newRoot: { _id: "$_id", source: {$objectToArray: "$$ROOT"}}
  }
},
{
  $lookup: {
    from: "address1", 
    localField: "_id", 
    foreignField: "_id",  
    as: "target"
  }
},
{
  $replaceRoot: { 
    newRoot: { _id: "$_id", source: "$source", target : {$objectToArray: { $first : "$target"}}}
  }
},
{
  $replaceRoot: {
    newRoot: { _id: "$_id", source: { $setDifference: ["$source","$target"]}, target: { $setDifference: ["$target","$source"]}}
  }
}
]);

如果集合在同一个数据库中，并且具有相同的“_id”，这将起作用。它可以很容易地修改以加入其他标准。

输出看起来像这样..

{ "_id" : ObjectId("5f8dc3abc6ff46000f023970"), "source" : [ { "k" : "postal_code", "v" : "" }, { "k" : "phone", "v" : "" } ], "target" : [ { "k" : "postal_code", "v" : null }, { "k" : "phone", "v" : null } ] }
{ "_id" : ObjectId("5f8dc3abc6ff46000f023971"), "source" : [ { "k" : "postal_code", "v" : "" }, { "k" : "phone", "v" : "" } ], "target" : [ { "k" : "postal_code", "v" : null }, { "k" : "phone", "v" : null } ] }
{ "_id" : ObjectId("5f8dc3abc6ff46000f023972"), "source" : [ { "k" : "postal_code", "v" : "" } ], "target" : [ { "k" : "postal_code", "v" : null } ] }
{ "_id" : ObjectId("5f8dc3abc6ff46000f023973"), "source" : [ { "k" : "postal_code", "v" : "" } ], "target" : [ { "k" : "postal_code", "v" : null } ] }
{ "_id" : ObjectId("5f8dc3abc6ff46000f023974"), "source" : [ { "k" : "address2", "v" : "" } ], "target" : [ { "k" : "address2", "v" : null } ] }
{ "_id" : ObjectId("5f8dc3abc6ff46000f023975"), "source" : [ { "k" : "address2", "v" : "" } ], "target" : [ { "k" : "address2", "v" : null } ] }
{ "_id" : ObjectId("5f8dc3abc6ff46000f023976"), "source" : [ { "k" : "address2", "v" : "" } ], "target" : [ { "k" : "address2", "v" : null } ] }
{ "_id" : ObjectId("5f8dc3abc6ff46000f023977"), "source" : [ { "k" : "address2", "v" : "" } ], "target" : [ { "k" : "address2", "v" : null } ] }
{ "_id" : ObjectId("5f8dc3abc6ff46000f023978"), "source" : [ { "k" : "address2", "v" : "" } ], "target" : [ { "k" : "address2", "v" : null } ] }
{ "_id" : ObjectId("5f8dc3abc6ff46000f023979"), "source" : [ { "k" : "address2", "v" : "" } ], "target" : [ { "k" : "address2", "v" : null } ] }
{ "_id" : ObjectId("5f8dc3abc6ff46000f02397a"), "source" : [ { "k" : "address2", "v" : "" } ], "target" : [ { "k" : "address2", "v" : null } ] }
{ "_id" : ObjectId("5f8dc3abc6ff46000f02397b"), "source" : [ { "k" : "address2", "v" : "" } ], "target" : [ { "k" : "address2", "v" : null } ] }
{ "_id" : ObjectId("5f8dc3abc6ff46000f02397c"), "source" : [ { "k" : "address2", "v" : "" } ], "target" : [ { "k" : "address2", "v" : null } ] }
{ "_id" : ObjectId("5f8dc3abc6ff46000f02397d"), "source" : [ { "k" : "address2", "v" : "" } ], "target" : [ { "k" : "address2", "v" : null } ] }
{ "_id" : ObjectId("5f8dc3abc6ff46000f02397e"), "source" : [ { "k" : "address2", "v" : "" } ], "target" : [ { "k" : "address2", "v" : null } ] }
{ "_id" : ObjectId("5f8dc3abc6ff46000f02397f"), "source" : [ { "k" : "address2", "v" : "" } ], "target" : [ { "k" : "address2", "v" : null } ] }
{ "_id" : ObjectId("5f8dc3abc6ff46000f023980"), "source" : [ { "k" : "address2", "v" : "" } ], "target" : [ { "k" : "address2", "v" : null } ] }
{ "_id" : ObjectId("5f8dc3abc6ff46000f023981"), "source" : [ { "k" : "address2", "v" : "" } ], "target" : [ { "k" : "address2", "v" : null } ] }
{ "_id" : ObjectId("5f8dc3abc6ff46000f023982"), "source" : [ { "k" : "address2", "v" : "" } ], "target" : [ { "k" : "address2", "v" : null } ] }
{ "_id" : ObjectId("5f8dc3abc6ff46000f023983"), "source" : [ { "k" : "address2", "v" : "" } ], "target" : [ { "k" : "address2", "v" : null } ] }
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【讨论】：