如何在mongo聚合管道中實現sql子查詢？

Question

如何將上面的sql子查詢轉換爲mongo聚合管道？select name，age from table1 where name in（select from table1 where age> 20）

如何將上述sql子查詢轉換爲mongo聚合管道？

Answer 1

考慮下面的示例數據：

db.collection.insert([ 
    { "name": "Peter", "age": 1 }, 
    { "name": "Peter", "age": 10 }, 
    { "name": "Peter", "age": 100 }, 
    { "name": "Paul", "age": 1 }, 
    { "name": "Mary", "age": 100 }, 
]) 

你可以做的是這樣的：

db.collection.aggregate({ 
    $group: { 
     "_id": "$name", // group by name 
     "docs": { $push: "$$ROOT" } // push all found documents into an array per group 
    } 
}, { 
    $match: { 
     "docs.age": { $gt: 5 } // eliminate all records that do not have at least one "age" entry that's greater than 5 
    } 
}, { 
    $unwind: "$docs" // flatten the group structure into multiple documents again 
}, { 
    $replaceRoot: { 
     "newRoot": "$docs" // restore original document layout 
    } 
}) 

...這將產生：

/* 1 */ 
{ 
    "_id" : ObjectId("59df15f9ad526e347ed9cda0"), 
    "name" : "Mary", 
    "age" : 100.0 
} 

/* 2 */ 
{ 
    "_id" : ObjectId("59df15f9ad526e347ed9cd9c"), 
    "name" : "Peter", 
    "age" : 1.0 
} 

/* 3 */ 
{ 
    "_id" : ObjectId("59df15f9ad526e347ed9cd9d"), 
    "name" : "Peter", 
    "age" : 10.0 
} 

/* 4 */ 
{ 
    "_id" : ObjectId("59df15f9ad526e347ed9cd9e"), 
    "name" : "Peter", 
    "age" : 100.0 
}