一、前言

MongoDB 虽说是文档型数据库,但是在学习和使用其语法时发现又与 MySQL 有些相似之处,在此记录点滴日后复习。

二、概念区别

比较 MySQL MongoDB
database database
table collection
row document
column field
索引 index index
表关联 table joins $lookup
主键 primary key primary key
聚合 aggregation aggregation pipeline

三、命令区别

比较 MySQL MongoDB
服务端 mysqld mongod
客户端 mysql mongo

四、关键字和函数区别

MySQL MongoDB
where $match
group by $group
having $match
select $project
order by $sort
limit $limit
sum() $sum
count() $sum
join $lookup

五、语句区别

5.1 表结构

5.1.1 创建表/集合

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db.people.insertOne( {
user_id: "abc123",
age: 55,
status: "A"
} )

相当于

CREATE TABLE people (
id MEDIUMINT NOT NULL AUTO_INCREMENT,
user_id Varchar(30),
age Number,
status char(1),
PRIMARY KEY (id)
)

5.1.2 新增字段

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db.people.updateMany(
{ },
{ $set: { join_date: new Date() } }
)

相当于 ALTER TABLE people ADD join_date DATETIME

5.1.3 删除字段

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db.people.updateMany(
{ },
{ $unset: { "join_date": "" } }
)

相当于 ALTER TABLE people DROP COLUMN join_date

5.1.4 创建索引

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db.people.createIndex( { user_id: 1 } )

相当于 CREATE INDEX idx_user_id_asc ON people(user_id)

5.1.5 删除表/集合

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db.people.drop()

相当于 DROP TABLE people

5.2 新增记录/文档

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db.people.insertOne(
{ user_id: "bcd001", age: 45, status: "A" }
)

相当于 INSERT INTO people(user_id,age,status) VALUES ("bcd001",45,"A")

5.3 查询记录/文档

5.3.1 简单查询

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db.people.find()

相当于 SELECT * FROM people
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db.people.find(
{ },
{ user_id: 1, status: 1 }
)

相当于 SELECT id,user_id,status FROM people
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db.people.find(
{ },
{ user_id: 1, status: 1, _id: 0 }
)

相当于 SELECT user_id, status FROM people

5.3.2 条件查询

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db.people.find(
{ status: "A" }
)

相当于 SELECT * FROM people WHERE status = "A"
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db.people.find(
{ status: "A" },
{ user_id: 1, status: 1, _id: 0 }
)

相当于 SELECT user_id, status FROM people WHERE status = "A"

5.3.3 非查询

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db.people.find(
{ status: { $ne: "A" } }
)

相当于 SELECT * FROM people WHERE status != "A"

5.3.4 且查询

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db.people.find(
{ status: "A",
age: 50 }
)

相当于 SELECT * FROM people WHERE status = "A" AND age = 50

5.3.5 或查询

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db.people.find(
{ $or: [ { status: "A" } ,
{ age: 50 } ] }
)

相当于 SELECT * FROM people WHERE status = "A" OR age = 50

5.3.6 大于查询

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db.people.find(
{ age: { $gt: 25 } }
)

相当于 SELECT * FROM people WHERE age > 25

5.3.7 小于查询

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db.people.find(
{ age: { $lt: 25 } }
)

相当于 SELECT * FROM people WHERE age < 25

5.3.8 范围查询

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db.people.find(
{ age: { $gt: 25, $lte: 50 } }
)

相当于 SELECT * FROM people WHERE age > 25 AND age <= 50

5.3.9 模糊查询

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db.people.find( { user_id: /bc/ } ) 或 db.people.find( { user_id: { $regex: /bc/ } } )

相当于 SELECT * FROM people WHERE user_id like "%bc%"
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db.people.find( { user_id: /^bc/ } ) 或 db.people.find( { user_id: { $regex: /^bc/ } } )

相当于 SELECT * FROM people WHERE user_id like "bc%"

5.3.10 排序查询

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db.people.find( { status: "A" } ).sort( { user_id: 1 } )

相当于 SELECT * FROM people WHERE status = "A" ORDER BY user_id ASC
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db.people.find( { status: "A" } ).sort( { user_id: -1 } )

相当于 SELECT * FROM people WHERE status = "A" ORDER BY user_id DESC

5.3.11 统计查询

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db.people.count() 或 db.people.find().count()

相当于 SELECT COUNT(*) FROM people
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db.people.count( { user_id: { $exists: true } } ) 或 db.people.find( { user_id: { $exists: true } } ).count()

相当于 SELECT COUNT(user_id) FROM people
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db.people.count( { age: { $gt: 30 } } ) 或 db.people.find( { age: { $gt: 30 } } ).count()

相当于 SELECT COUNT(*) FROM people WHERE age > 30

5.3.12 去重查询

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db.people.distinct( "status" )

相当于 SELECT DISTINCT(status) FROM people

5.3.13 分页查询

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db.people.findOne() 或 db.people.find().limit(1)

相当于 SELECT * FROM people LIMIT 1
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db.people.find().limit(5).skip(10)

相当于 SELECT * FROM people LIMIT 5 SKIP 10

5.3.14 查询计划

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db.people.find( { status: "A" } ).explain()

相当于 EXPLAIN SELECT * FROM people WHERE status = "A"

5.4 修改记录/文档

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db.people.updateMany(
{ age: { $gt: 25 } },
{ $set: { status: "C" } }
);

相当于 UPDATE people SET status = "C" WHERE age > 25;

db.people.updateMany(
{ status: "A" } ,
{ $inc: { age: 3 } }
);

相当于 UPDATE people SET age = age + 3 WHERE status = "A";

5.5 删除记录/文档

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db.people.deleteMany( { status: "D" } );

相当于 DELETE FROM people WHERE status = "D";

db.people.deleteMany({});

相当于 DELETE FROM people;

六、参考资料