mongodb中同一集合上的联合 [英] union on same collection in mongodb

问题描述

我需要采用以下结构来搜索文档的最可行的方法.

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

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

以sql方式，我需要的结果集将是这三个的UNION(n个记录按var1排序，n个记录按var2排序，n个记录按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)

使用UNION，我希望将重复项删除.

with UNION I expect the duplicates to be removed.

作为mongodb的新手，我无法找到正确的方法来编写此类操作的查询，我相信在mongodb中一定是有可能的.

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.

如果无法实现，请提出一个替代的nosql解决方案.

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

推荐答案

与您正在寻找的最接近的MongoDB运算符是

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}
)

由于您只能查询一个集合，因此结果将已经在文档级别上进行重复数据删除，并且如果指定了结果，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将结果集合并到应用程序代码中.

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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