mongodb 中同一个集合的联合 [英] union on same collection in mongodb

问题描述

我需要最可行的方法来搜索具有以下结构的文档.

I need the most viable way to search docs with the following structure.

{ _id:"",
var1: number,
var2: number,
var3: number,
}

在sql方式中，我需要的结果集是这三个的联合(n条记录按var1排序，n条记录按var2排序，n条记录按var3排序)

In the sql way the resultset i need would be UNION of these three (n records sorted by var1,n records sorted by var2,n records sorted by var3)

对于 UNION，我希望删除重复项.

with UNION I expect the duplicates to be removed.

作为 mongodb 的新手，我无法找到为此类操作编写查询的正确方法，我相信这在 mongodb 中一定是可能的.

Being new to mongodb i am not able to find the right way to write a query for such an operation, i believe it must be possible in mongodb.

如果不可能，请您建议一个替代的 nosql 解决方案.

If in case its not possible, could you please suggest an alternate nosql solution.

推荐答案

最接近您正在寻找的 MongoDB 运算符是 $or，但这与 SQL UNION 将两个单独的查询合并为一个结果.MongoDB 查询始终针对单个集合，但 $or 允许您有多个查询子句.

The closest MongoDB operator to what you are looking for is an $or, but that isn't quite the same as an SQL UNION which combines two separate queries into a single result. MongoDB queries are always against a single collection, but $or allows you to have multiple query clauses.

例如:

db.collection.find(
    // Find documents matching any of these values
    {$or:[
        {var1: 123},
        {var2: 456},
        {var3: 789}
    ]}
).sort(
    // Sort in ascending order
    {var1:1, var2:1, var3:1}
)

由于您只能查询单个集合，因此结果将已在文档级别进行重复数据删除，并且如果指定了所有结果，则所有结果将共享相同的排序顺序.

Since you are limited to querying a single collection, results will already be de-duplicated at the document level and all results will share the same sort order if one is specified.

如果要在 MongoDB 中模拟 UNION(或其他处理多个集合/查询的操作)，则必须编写多个查询并在应用程序代码中合并结果集.

If you want to simulate a UNION (or other operation working with multiple collections/queries) in MongoDB, you will have to write multiple queries and merge the result sets in your application code.

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