MongoDB 提供了丰富的操作符（Operators）和运算符（Expressions）用于在查询和更新文档时指定条件和操作数据。

查询操作符（Query Operators）

$eq - 等于

db.collection.find({ field: { $eq: value } })
// 示例：查找所有名字等于 "Tom" 的文档
db.users.find({ name: { $eq: "Tom" } })

$gt - 大于

db.collection.find({ field: { $gt: value } })
// 示例：查找所有年龄大于 25 的用户
db.users.find({ age: { $gt: 25 } })

$gte - 大于等于

db.collection.find({ field: { $gte: value } })
// 示例：查找所有年龄大于等于 25 的用户
db.users.find({ age: { $gte: 25 } })

$lt - 小于

db.collection.find({ field: { $lt: value } })
// 示例：查找所有年龄小于 25 的用户
db.users.find({ age: { $lt: 25 } })

$lte - 小于等于

db.collection.find({ field: { $lte: value } })
// 示例：查找所有年龄小于等于 25 的用户
db.users.find({ age: { $lte: 25 } })

$ne - 不等于

db.collection.find({ field: { $ne: value } })
// 示例：查找所有名字不是 "Tom" 的文档
db.users.find({ name: { $ne: "Tom" } })

$in - 在数组中

db.collection.find({ field: { $in: array } })
// 示例：查找兴趣包含 "阅读" 或 "游泳" 的用户
db.users.find({ interests: { $in: ["阅读", "游泳"] } })

$nin - 不在数组中

db.collection.find({ field: { $nin: array } })
// 示例：查找兴趣不含 "阅读" 和 "游泳" 的用户
db.users.find({ interests: { $nin: ["阅读", "游泳"] } })

$or - 或者

db.collection.find({ $or: [{ condition1 }, { condition2 }] })
// 示例：查找名字为 "Tom" 或年龄大于 25 的用户
db.users.find({ $or: [{ name: "Tom" }, { age: { $gt: 25 } }] })

$and - 并且

db.collection.find({ $and: [{ condition1 }, { condition2 }] })
// 示例：查找名字为 "Tom" 并且年龄大于 25 的用户
db.users.find({ $and: [{ name: "Tom" }, { age: { $gt: 25 } }] })

$not - 非

db.collection.find({ field: { $not: { operator: value } } })
// 示例：查找年龄不小于 25 的用户
db.users.find({ age: { $not: { $lt: 25 } } })

$exists - 字段存在

db.collection.find({ field: { $exists: true or false } })
// 示例：查找有 `email` 字段的用户
db.users.find({ email: { $exists: true } })

更新操作符（Update Operators）

$set - 设置字段的值

db.collection.update({ query }, { $set: { field: value } })
// 示例：更新名字为 "Tom" 的用户的年龄为 30
db.users.update({ name: "Tom" }, { $set: { age: 30 } })

$unset - 删除字段

db.collection.update({ query }, { $unset: { field: "" } })
// 示例：删除名字为 "Tom" 的用户的 `age` 字段
db.users.update({ name: "Tom" }, { $unset: { age: "" } })

$inc - 增加数值字段的值

db.collection.update({ query }, { $inc: { field: value } })
// 示例：将名字为 "Tom" 的用户的年龄增加 2
db.users.update({ name: "Tom" }, { $inc: { age: 2 } })

$push - 向数组字段添加元素

db.collection.update({ query }, { $push: { field: value } })
// 示例：向名字为 "Tom" 的用户的兴趣列表添加 "足球"
db.users.update({ name: "Tom" }, { $push: { interests: "足球" } })

$pull - 从数组字段删除元素

db.collection.update({ query }, { $pull: { field: value } })
// 示例：从名字为 "Tom" 的用户的兴趣列表中删除 "足球"
db.users.update({ name: "Tom" }, { $pull: { interests: "足球" } })

$addToSet - 向数组添加元素，但不创建重复项

db.collection.update({ query }, { $addToSet: { field: value } })
// 示例：向名字为 "Tom" 的用户的兴趣列表中添加 "游泳"，如果 "游泳" 已存在，则忽略
db.users.update({ name: "Tom" }, { $addToSet: { interests: "游泳" } })

$each - 与 $push 或 $addToSet 配合，向数组添加多个元素

db.collection.update({ query }, { $push: { field: { $each: [value1, value2] } } })
// 示例：一次性向名字为 "Tom" 的用户的兴趣列表中添加多个兴趣
db.users.update({ name: "Tom" }, { $push: { interests: { $each: ["绘画", "舞蹈"] } } })

$pop - 从数组的开头或末尾删除元素

// $pop: 1 从末尾移除，$pop: -1 从开头移除
db.collection.update({ query }, { $pop: { field: 1 or -1 } })
// 示例：从名字为 "Tom" 的用户的兴趣列表末尾删除一个兴趣
db.users.update({ name: "Tom" }, { $pop: { interests: 1 } })

聚合管道操作符（Aggregation Pipeline Operators）

$match - 过滤数据

db.collection.aggregate([ { $match: { field: value } } ])
// 示例：筛选所有年龄大于 25 的用户
db.users.aggregate([ { $match: { age: { $gt: 25 } } }])

$group - 按字段分组

db.collection.aggregate([
  { $group: { _id: "$field", count: { $sum: 1 } } }
])
// 示例：按兴趣分组计数用户
db.users.aggregate([
  { $group: { _id: "$interests", count: { $sum: 1 } } }
])

$project - 指定输出字段

db.collection.aggregate([ { $project: { field1: 1, field2: 0 } } ])
// 示例：输出用户的名字和兴趣，不输出其他字段
db.users.aggregate([ { $project: { name: 1, interests: 1 } }])

$sort - 排序

db.collection.aggregate([ { $sort: { field: 1 or -1 } } ])
// 1 代表升序, -1 代表降序
// 示例：按年龄升序排列用户
db.users.aggregate([ { $sort: { age: 1 } }])

以上是MongoDB中的一些常用操作符和运算符，它们可以帮你构建灵活和强大的数据操作指令。在实际的应用中，会将多个操作符组合起来使用，以满足复杂的业务逻辑。

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English version

Detailed Introduction to MongoDB Operators and Expressions

MongoDB offers a rich set of operators (Operators) and expressions (Expressions) for specifying conditions and manipulating data when querying and updating documents.

Query Operators

$eq - Equal

db.collection.find({ field: { $eq: value } })
// Example: Find all documents where the name is equal to "Tom"
db.users.find({ name: { $eq: "Tom" } })

$gt - Greater Than

db.collection.find({ field: { $gt: value } })
// Example: Find all users older than 25
db.users.find({ age: { $gt: 25 } })

$gte - Greater Than or Equal To

db.collection.find({ field: { $gte: value } })
// Example: Find all users aged 25 or older
db.users.find({ age: { $gte: 25 } })

$lt - Less Than

db.collection.find({ field: { $lt: value } })
// Example: Find all users younger than 25
db.users.find({ age: { $lt: 25 } })

$lte - Less Than or Equal To

db.collection.find({ field: { $lte: value } })
// Example: Find all users aged 25 or younger
db.users.find({ age: { $lte: 25 } })

$ne - Not Equal

db.collection.find({ field: { $ne: value } })
// Example: Find all documents where the name is not "Tom"
db.users.find({ name: { $ne: "Tom" } })

$in - In an Array

db.collection.find({ field: { $in: array } })
// Example: Find users whose interests include "Reading" or "Swimming"
db.users.find({ interests: { $in: ["Reading", "Swimming

"] } })

$nin - Not in an Array

db.collection.find({ field: { $nin: array } })
// Example: Find users whose interests do not include "Reading" and "Swimming"
db.users.find({ interests: { $nin: ["Reading", "Swimming"] } })

$or - Or

db.collection.find({ $or: [{ condition1 }, { condition2 }] })
// Example: Find users who are either named "Tom" or are older than 25
db.users.find({ $or: [{ name: "Tom" }, { age: { $gt: 25 } }] })

$and - And

db.collection.find({ $and: [{ condition1 }, { condition2 }] })
// Example: Find users who are named "Tom" and are older than 25
db.users.find({ $and: [{ name: "Tom" }, { age: { $gt: 25 } }] })

$not - Not

db.collection.find({ field: { $not: { operator: value } } })
// Example: Find users who are not younger than 25
db.users.find({ age: { $not: { $lt: 25 } } })

$exists - Field Exists

db.collection.find({ field: { $exists: true or false } })
// Example: Find users who have an `email` field
db.users.find({ email: { $exists: true } })

Update Operators

$set - Set the Value of a Field

db.collection.update({ query }, { $set: { field: value } })
// Example: Update the age of users named "Tom" to 30
db.users.update({ name: "Tom" }, { $set: { age: 30 } })

$unset - Remove a Field

db.collection.update({ query }, { $unset: { field: "" } })
// Example: Remove the `age` field from users named "Tom"
db.users.update({ name: "Tom" }, { $unset: { age: "" } })

$inc - Increment a Numeric Field's Value

db.collection.update({ query }, { $inc: { field: value } })
// Example: Increment the age of users named "Tom" by 2
db.users.update({ name: "Tom" }, { $inc: { age: 2 } })

$push - Add an Element to an Array Field

db.collection.update({ query }, { $push: { field: value } })
// Example: Add "Football" to the interests list of users named "Tom"
db.users.update({ name: "Tom" }, { $push: { interests: "Football" } })

$pull - Remove an Element from an Array Field

db.collection.update({ query }, { $pull: { field: value } })
// Example: Remove "Football" from the interests list of users named "Tom"
db.users.update({ name: "Tom" }, { $pull: { interests: "Football" } })

$addToSet - Add an Element to an Array without Creating Duplicates

db.collection.update({ query }, { $addToSet: { field: value } })
// Example: Add "Swimming" to the interests list of users named "Tom", if "Swimming" isn't already

present
db.users.update({ name: "Tom" }, { $addToSet: { interests: "Swimming" } })

$each - Combined with $push or $addToSet, Add Multiple Elements to an Array

db.collection.update({ query }, { $push: { field: { $each: [value1, value2] } } })
// Example: Add multiple interests at once to the interests list of users named "Tom"
db.users.update({ name: "Tom" }, { $push: { interests: { $each: ["Painting", "Dancing"] } } })

$pop - Remove an Element from the Beginning or End of an Array

// $pop: 1 removes from the end, $pop: -1 removes from the beginning
db.collection.update({ query }, { $pop: { field: 1 or -1 } })
// Example: Remove an interest from the end of the interests list of users named "Tom"
db.users.update({ name: "Tom" }, { $pop: { interests: 1 } })

Aggregation Pipeline Operators

$match - Filter Data

db.collection.aggregate([ { $match: { field: value } } ])
// Example: Filter all users older than 25
db.users.aggregate([ { $match: { age: { $gt: 25 } } }])

$group - Group by Field

db.collection.aggregate([
  { $group: { _id: "$field", count: { $sum: 1 } } }
])
// Example: Group users by interests and count them
db.users.aggregate([
  { $group: { _id: "$interests", count: { $sum: 1 } } }
])

$project - Specify Output Fields

db.collection.aggregate([ { $project: { field1: 1, field2: 0 } } ])
// Example: Output user names and interests, excluding other fields
db.users.aggregate([ { $project: { name: 1, interests: 1 } }])

$sort - Sort

db.collection.aggregate([ { $sort: { field: 1 or -1 } } ])
// 1 for ascending order, -1 for descending