MongoDB學習筆記（3）- Mongo Shell 常用查詢命令

MongoDB學習筆記（3）- Mongo Shell 常用查詢命令

本文所使用的MongoDB版本爲 4.0.10

> db.version();
4.0.10

一、find 命令進行簡查詢

find( 查詢條件 ，返回的字段)， 

1. 查詢時返回所有字段

db.user.find() --> 查詢user集合中所有的數據

> db.user.find()
{ "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom", "age" : 12, "tel" : "10086" }
{ "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30 }
{ "_id" : ObjectId("5d2f103414077ad0dab139c8"), "username" : "Martin", "age" : 40 }
{ "_id" : ObjectId("5d2f105414077ad0dab139c9"), "username" : "kart", "age" : 50 }

db.user.find( {"username":"Mary"} ) --> 列出username=Mary的數據

> db.user.find({"username": "Mary"})
{ "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30 }

db.user.find( {"age":50} ) --> 列出 age = 50 的數據

> db.user.find( {"age":50} )
{ "_id" : ObjectId("5d2f105414077ad0dab139c9"), "username" : "kart", "age" : 50 }

2. 查詢時只返回指定幾個字段

db.user.find({}, {"username":1}) --> 列出所有人的 username 字段

> db.user.find({}, {"username": 1})
{ "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom" }
{ "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary" }
{ "_id" : ObjectId("5d2f103414077ad0dab139c8"), "username" : "Martin" }
{ "_id" : ObjectId("5d2f105414077ad0dab139c9"), "username" : "kart" }

db.user.find({}, {"tel": 1}) --> 列出所有人的 tel 字段

> db.user.find({}, {"tel": 1})
{ "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "tel" : "10086" }
{ "_id" : ObjectId("5d2f102414077ad0dab139c7") }
{ "_id" : ObjectId("5d2f103414077ad0dab139c8") }
{ "_id" : ObjectId("5d2f105414077ad0dab139c9") }

db.user.find({} , {"age": 0} ) --> 除了age字段，其他字段都列出來

> db.user.find({}, {"age": 0})
{ "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom", "tel" : "10086" }
{ "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary" }
{ "_id" : ObjectId("5d2f103414077ad0dab139c8"), "username" : "Martin" }
{ "_id" : ObjectId("5d2f105414077ad0dab139c9"), "username" : "kart" }

二、常用操作符

1. $lt (<)

查詢年齡小於30歲的用戶

> db.user.find( {"age": { $lt: 30 } } )
{ "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom", "age" : 12, "tel" : "10086" }

2. $lte (<=)

查詢年齡小於等於30歲的用戶

> db.user.find( {"age": { $lte: 30 } } )
{ "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom", "age" : 12, "tel" : "10086" }
{ "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30 }

3. $gt (>)

查詢年齡大於30歲的用戶

> db.user.find( {"age": { $gt: 30 } } )
{ "_id" : ObjectId("5d2f103414077ad0dab139c8"), "username" : "Martin", "age" : 40 }
{ "_id" : ObjectId("5d2f105414077ad0dab139c9"), "username" : "kart", "age" : 50 }

4. $gte (>= )

查詢年齡大於等於30歲的用戶

> db.user.find( {"age": { $gte: 30 } } )
{ "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30 }
{ "_id" : ObjectId("5d2f103414077ad0dab139c8"), "username" : "Martin", "age" : 40 }
{ "_id" : ObjectId("5d2f105414077ad0dab139c9"), "username" : "kart", "age" : 50 }

5. $ne ( <> )

查詢年齡不等於30歲的用戶

> db.user.find( {"age": { $ne: 30 } } )
{ "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom", "age" : 12, "tel" : "10086" }
{ "_id" : ObjectId("5d2f103414077ad0dab139c8"), "username" : "Martin", "age" : 40 }
{ "_id" : ObjectId("5d2f105414077ad0dab139c9"), "username" : "kart", "age" : 50 }

6. $and (AND)

查詢年齡大於10歲且小於40歲的用戶

> db.user.find( { $and: [ { "age": { $lt: 40 } }  , {"age": { $gt: 10 } } ] } )
{ "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom", "age" : 12, "tel" : "10086" }
{ "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30, "tel" : null }

7. $or (OR)

查詢年齡小於20歲或者大於40歲的用戶

> db.user.find( { $or: [ { "age": { $lt: 20 } }  , {"age": { $gt:40 } } ] } )
{ "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom", "age" : 12, "tel" : "10086" }
{ "_id" : ObjectId("5d2f105414077ad0dab139c9"), "username" : "kart", "age" : 50 }

8. $in (IN)

查詢年齡爲 20, 30, 40 歲的用戶

> db.user.find( { "age" : { $in : [20, 30, 40] } } )
{ "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30 }
{ "_id" : ObjectId("5d2f103414077ad0dab139c8"), "username" : "Martin", "age" : 40 }

9. $not (NOT)

查詢年齡不是 20, 40 歲的用戶（$not）

> db.user.find( { "age" : { $not: { $in : [20, 40] } } } )
{ "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom", "age" : 12, "tel" : "10086" }
{ "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30 }
{ "_id" : ObjectId("5d2f105414077ad0dab139c9"), "username" : "kart", "age" : 50 }

10. $nin (NOT IN)

查詢年齡不是 20, 40 歲的用戶

> db.user.find( { "age" : { $nin : [20, 40] } } )
{ "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom", "age" : 12, "tel" : "10086" }
{ "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30 }
{ "_id" : ObjectId("5d2f105414077ad0dab139c9"), "username" : "kart", "age" : 50 }

11. $mod (取模)

查詢年齡對 4 取模餘 2 的用戶

> db.user.find( {"age" : { $mod : [4, 2] } } )
{ "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30 }
{ "_id" : ObjectId("5d2f105414077ad0dab139c9"), "username" : "kart", "age" : 50 }

12. $exists (存在)

$exists 用於判斷鍵是否

給 Mary 添加 tel 字段，值設爲 null

> db.user.update({ "username": "Mary" }, { $set : { "tel" : null } })
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.user.find()
{ "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom", "age" : 12, "tel" : "10086" }
{ "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30, "tel" : null }
{ "_id" : ObjectId("5d2f103414077ad0dab139c8"), "username" : "Martin", "age" : 40 }
{ "_id" : ObjectId("5d2f105414077ad0dab139c9"), "username" : "kart", "age" : 50 }

列出存在 tel 字段的記錄

> db.user.find({ "tel" : { $exists : 1 }})
{ "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom", "age" : 12, "tel" : "10086" }
{ "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30, "tel" : null }

判斷值爲 null 時要注意：
db.user.find({ "friends" : null })
該命令不僅查出值爲null的記錄，friends 鍵不存在的記錄也會被取出來。

> db.user.find({ "tel" : null })
{ "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30, "tel" : null }
{ "_id" : ObjectId("5d2f103414077ad0dab139c8"), "username" : "Martin", "age" : 40 }
{ "_id" : ObjectId("5d2f105414077ad0dab139c9"), "username" : "kart", "age" : 50 }

如果想取出 friends 鍵存在，並且值爲 null 的記錄應該這樣來取：

> db.user.find( { $and: [ { "tel" : null }, { "tel" : {$exists: 1 } } ] } )
{ "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30, "tel" : null }

13. $where

$where : 根據函數返回值來判斷是否返回數據

取出 年齡 * 3 + 5 小於 100 用戶的

db.user.find( { $where : function(){ 
    return (this.age * 3 + 5 < 100); 
} } );

> db.user.find( { $where : function(){ return (this.age * 3 + 5 < 100); } } );
{ "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom", "age" : 12, "tel" : "10086" }
{ "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30, "tel" : null }

this 代表當前這個記錄。

通過這個 $where 基本可以實現任意類型的查詢。不過不到必要時候不要用這個方法，因爲它的速度比一般查詢要慢很多。

三、使用正則查詢

查找名字中含有 "art" 的記錄

> db.user.find( { "username" : /art/ } )
{ "_id" : ObjectId("5d2f103414077ad0dab139c8"), "username" : "Martin", "age" : 40 }
{ "_id" : ObjectId("5d2f105414077ad0dab139c9"), "username" : "kart", "age" : 50 }

查找以名稱以 "mar" 開頭且不區分大小寫的記錄

> db.user.find( {"username": /^mar/i } );
{ "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30, "tel" : null }
{ "_id" : ObjectId("5d2f103414077ad0dab139c8"), "username" : "Martin", "age" : 40 }

四、查詢數組

1. $all：判斷某個數組類型字段包含的多個指定值時。

給 user 集合中的用戶添加一些朋友，結果如下：

> db.user.find()
{ "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom", "age" : 12, "tel" : "10086", "friend" : [ "Mary", "Jocker", "Martin", "Kart" ] }
{ "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30, "tel" : null, "friend" : [ "Jocker", "Martin" ] }
{ "_id" : ObjectId("5d2f103414077ad0dab139c8"), "username" : "Martin", "age" : 40, "friend" : [ "Mary", "Jocker", "Kart" ] }
{ "_id" : ObjectId("5d2f105414077ad0dab139c9"), "username" : "kart", "age" : 50 }

取出 friend 數組中既有 Mary 又有 Jocker 的記錄

> db.user.find({ "friend": { $all : ["Mary", "Jocker"] } })
{ "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom", "age" : 12, "tel" : "10086", "friend" : [ "Mary", "Jocker", "Martin", "Kart" ] }
{ "_id" : ObjectId("5d2f103414077ad0dab139c8"), "username" : "Martin", "age" : 40, "friend" : [ "Mary", "Jocker", "Kart" ] }

2. $size：查詢擁有指定元素個數的數組

取出 friend 數組中有3個值的記錄

> db.user.find( { "friend" : { $size  : 3 } } )
{ "_id" : ObjectId("5d2f103414077ad0dab139c8"), "username" : "Martin", "age" : 40, "friend" : [ "Mary", "Jocker", "Kart" ] }

3. $slice : 返回一個數組的子集

{$slice : 10} --> 數組中的前10個
{$slice : -10} --> 數組中的後10個
{$slice : [20, 10] } --> 從數組中下標爲20的元素開始，向後去除10個元素

取出Tom的前3個朋友

> db.user.find( {"username": "Tom"}, { "friend" : {$slice : 3} } )
{ "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom", "age" : 12, "tel" : "10086", "friend" : [ "Mary", "Jocker", "Martin" ] }

五、查詢內嵌文檔

1. $elemMatch

如有這樣的數據結構：
有個comments字段，該字段是一個數組，每一項是一個內嵌的comment對象

{
    "_id": ObjectId("5d31b1d24fd0d7ad0a1a1361"),
    "author": "Tom",
    "content": "I am Tom!",
    "comments": [{
        "user": "Mary",
        "score": 3,
        "comment": "Nice!"
    }, {
        "user": "Martin",
        "score": 6,
        "comment": "I'm reading..."
    }, {
        "user": "Jocker",
        "score": 8,
        "comment": "You're kidding me"
    }]
}
{
    "_id": ObjectId("5d31b3114fd0d7ad0a1a1364"),
    "author": "Martin",
    "content": "I am Martin!",
    "comments": [{
        "user": "Tom",
        "score": 5,
        "comment": "Nice!"
    }, {
        "user": "Mary",
        "score": 6,
        "comment": "I'm reading..."
    }, {
        "user": "Jocker",
        "score": 3,
        "comment": "You're kidding me"
    }]
}
{
    "_id": ObjectId("5d31b3314fd0d7ad0a1a1365"),
    "author": "Mary",
    "content": "I am Mary!",
    "comments": [{
        "user": "Tom",
        "score": 3,
        "comment": "Nice!"
    }, {
        "user": "Martin",
        "score": 5,
        "comment": "I'm reading..."
    }, {
        "user": "Jocker",
        "score": 2,
        "comment": "You're kidding me"
    }]
}

查詢評論中包含 score 大於5的文章記錄

> db.blog.find ({ "comments" : { "$elemMatch" : { "score" : {"$gt" : 5}}} })
{ "_id" : ObjectId("5d31b1d24fd0d7ad0a1a1361"), "author" : "Tom", "content" : "I am Tom!", "comments" : [ { "user" : "Mary", "score" : 3, "comment" : "Nice!" }, { "user" : "Martin", "score" : 6, "comment" : "I'm reading..." }, { "user" : "Jocker", "score" : 8, "comment" : "You're kidding me" } ] }
{ "_id" : ObjectId("5d31b3114fd0d7ad0a1a1364"), "author" : "Martin", "content" : "I am Martin!", "comments" : [ { "user" : "Tom", "score" : 5, "comment" : "Nice!" }, { "user" : "Mary", "score" : 6, "comment" : "I'm reading..." }, { "user" : "Jocker", "score" : 3, "comment" : "You're kidding me" } ] }

查詢Tom的文章的評論中 score 大於 5 的評論記錄

> db.blog.find ({"author": "Tom"}, { "comments" : { "$elemMatch" : { "score" : {"$gt" : 3}}} })
{ "_id" : ObjectId("5d31b1d24fd0d7ad0a1a1361"), "comments" : [ { "user" : "Martin", "score" : 6, "comment" : "I'm reading..." } ] }