一、find 命令进行简查询
find( 查询条件 ,返回的字段),
1. 查询时返回所有字段
db.user.find() --> 查询user集合中所有的数据
> 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的数据
> db.user.find({"username": "Mary"}) { "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30 }
db.user.find( {"age":50} ) --> 列出 age = 50 的数据
> db.user.find( {"age":50} ) { "_id" : ObjectId("5d2f105414077ad0dab139c9"), "username" : "kart", "age" : 50 }
2. 查询时只返回指定几个字段
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,其他字段都列出来
> 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 (<)
查询年龄小于30岁的用户
> db.user.find( {"age": { $lt: 30 } } ) { "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom", "age" : 12, "tel" : "10086" }
2. $lte (<=)
查询年龄小于等于30岁的用户
> db.user.find( {"age": { $lte: 30 } } ) { "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom", "age" : 12, "tel" : "10086" } { "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30 }
3. $gt (>)
查询年龄大于30岁的用户
> db.user.find( {"age": { $gt: 30 } } ) { "_id" : ObjectId("5d2f103414077ad0dab139c8"), "username" : "Martin", "age" : 40 } { "_id" : ObjectId("5d2f105414077ad0dab139c9"), "username" : "kart", "age" : 50 }
4. $gte (>= )
查询年龄大于等于30岁的用户
> 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 ( <> )
查询年龄不等于30岁的用户
> 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)
查询年龄大于10岁且小于40岁的用户
> 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)
查询年龄小于20岁或者大于40岁的用户
> 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)
查询年龄为 20, 30, 40 岁的用户
> db.user.find( { "age" : { $in : [20, 30, 40] } } ) { "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30 } { "_id" : ObjectId("5d2f103414077ad0dab139c8"), "username" : "Martin", "age" : 40 }
9. $not (NOT)
查询年龄不是 20, 40 岁的用户($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)
查询年龄不是 20, 40 岁的用户
> 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)
查询年龄对 4 取模余 2 的用户
> 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 用于判断键是否
给 Mary 添加 tel 字段,值设为 null
> db.user.find( {"age" : { $mod : [4, 2] } } ) { "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30 } { "_id" : ObjectId("5d2f105414077ad0dab139c9"), "username" : "kart", "age" : 50 }
列出存在 tel 字段的记录
> db.user.find({ "tel" : { $exists : 1 }}) { "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom", "age" : 12, "tel" : "10086" } { "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30, "tel" : null }
判断值为 null 时要注意:
db.user.find({ "friends" : null })
该命令不仅查出值为null的记录,friends 键不存在的记录也会被取出来。
> 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 键存在,并且值为 null 的记录应该这样来取:
> db.user.find( { $and: [ { "tel" : null }, { "tel" : {$exists: 1 } } ] } ) { "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30, "tel" : null }
13. $where
$where : 根据函数返回值来判断是否返回数据
取出 年龄 * 3 + 5 小于 100
用户的
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
代表当前这个记录。通过这个 $where 基本可以实现任意类型的查询。不过不到必要时候不要用这个方法,因为它的速度比一般查询要慢很多。
三、使用正则查询
查找名字中含有 "art" 的记录
> db.user.find( { "username" : /art/ } ) { "_id" : ObjectId("5d2f103414077ad0dab139c8"), "username" : "Martin", "age" : 40 } { "_id" : ObjectId("5d2f105414077ad0dab139c9"), "username" : "kart", "age" : 50 }
查找以名称以 "mar" 开头且不区分大小写的记录
> db.user.find( {"username": /^mar/i } ); { "_id" : ObjectId("5d2f102414077ad0dab139c7"), "username" : "Mary", "age" : 30, "tel" : null } { "_id" : ObjectId("5d2f103414077ad0dab139c8"), "username" : "Martin", "age" : 40 }
四、查询数组
1. $all:判断某个数组类型字段包含的多个指定值时。
给 user 集合中的用户添加一些朋友,结果如下:
> 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 数组中既有 Mary 又有 Jocker 的记录
> 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:查询拥有指定元素个数的数组
取出 friend 数组中有3个值的记录
> db.user.find( { "friend" : { $size : 3 } } ) { "_id" : ObjectId("5d2f103414077ad0dab139c8"), "username" : "Martin", "age" : 40, "friend" : [ "Mary", "Jocker", "Kart" ] }
3. $slice : 返回一个数组的子集
{$slice : 10} --> 数组中的前10个 {$slice : -10} --> 数组中的后10个 {$slice : [20, 10] } --> 从数组中下标为20的元素开始,向后去除10个元素
取出Tom的前3个朋友
> db.user.find( {"username": "Tom"}, { "friend" : {$slice : 3} } ) { "_id" : ObjectId("5d2f0a4714077ad0dab139c5"), "username" : "Tom", "age" : 12, "tel" : "10086", "friend" : [ "Mary", "Jocker", "Martin" ] }
五、查询内嵌文档
1. $elemMatch
如有这样的数据结构:
有个comments字段,该字段是一个数组,每一项是一个内嵌的comment对象
{ "_id": ObjectId("5d31b1d24fd0d7ad0a1a1361"), "author": "Tom", "content": "I am Tom!", "comments": [{ "user": "Mary", "score": 3, "comment": "Nice!" }, { "user": "Martin", "score": 6, "comment": "I'm reading..." }, { "user": "Jocker", "score": 8, "comment": "You're kidding me" }] } { "_id": ObjectId("5d31b3114fd0d7ad0a1a1364"), "author": "Martin", "content": "I am Martin!", "comments": [{ "user": "Tom", "score": 5, "comment": "Nice!" }, { "user": "Mary", "score": 6, "comment": "I'm reading..." }, { "user": "Jocker", "score": 3, "comment": "You're kidding me" }] } { "_id": ObjectId("5d31b3314fd0d7ad0a1a1365"), "author": "Mary", "content": "I am Mary!", "comments": [{ "user": "Tom", "score": 3, "comment": "Nice!" }, { "user": "Martin", "score": 5, "comment": "I'm reading..." }, { "user": "Jocker", "score": 2, "comment": "You're kidding me" }] }
查询评论中包含 score 大于5的文章记录
> db.blog.find ({ "comments" : { "$elemMatch" : { "score" : {"$gt" : 5}}} }) { "_id" : ObjectId("5d31b1d24fd0d7ad0a1a1361"), "author" : "Tom", "content" : "I am Tom!", "comments" : [ { "user" : "Mary", "score" : 3, "comment" : "Nice!" }, { "user" : "Martin", "score" : 6, "comment" : "I'm reading..." }, { "user" : "Jocker", "score" : 8, "comment" : "You're kidding me" } ] } { "_id" : ObjectId("5d31b3114fd0d7ad0a1a1364"), "author" : "Martin", "content" : "I am Martin!", "comments" : [ { "user" : "Tom", "score" : 5, "comment" : "Nice!" }, { "user" : "Mary", "score" : 6, "comment" : "I'm reading..." }, { "user" : "Jocker", "score" : 3, "comment" : "You're kidding me" } ] }
查询Tom的文章的评论中 score 大于 5 的评论记录
> db.blog.find ({"author": "Tom"}, { "comments" : { "$elemMatch" : { "score" : {"$gt" : 3}}} }) { "_id" : ObjectId("5d31b1d24fd0d7ad0a1a1361"), "comments" : [ { "user" : "Martin", "score" :