MongoDB notes (5)-query documents

grammar:

db.collection.find(query, projection)

• Parameter Description
  • query : optional, use query operators to specify query conditions
  • projection : optional, use the projection operator to specify the returned key. All the key values ​​in the document will be returned during the query. You only need to omit this parameter (default is omitted).

format:

> db.demo.find().pretty()

Operator query:

• Greater than: (greater than>) $ gt
• Greater than or equal to: (gt equal> =) $ gte
• Less than: (less than <) $ lt
• Less than or equal to: (lt equal <=) $ lte
• Match: (equal =) $ eq
• Mismatch: (not equal! =) $ Ne
• Contains: (like) / val1 /
• Beginning: (like) / ^ val1 /
• End: (like) / val1 $ /

MongoDB and RDBMS Where statement comparison

If you are familiar with regular SQL data, the following table can better understand MongoDB's conditional query:

operating	format	example	Similar statements in RDBMS
more than the	{<key>:{$gt:<val>}}	db.demo.find({"age":{$gt:20}}).pretty()	where age > 20
greater than or equal to	{<key>:{$gte:<val>}}	db.demo.find({"age":{$gte:20}}).pretty()	where age >= 20
Less than	{<key>:{$lt:<val>}}	db.demo.find({"age":{$lt:20}}).pretty()	where age < 20
less than or equal to	{<key>:{$lte:<val>}}	db.demo.find({"age":{$lte:20}}).pretty()	where age <= 20
equal	{<key>:<val>}	db.demo.find({"name":"yourName"}).pretty()	where name = 'yourName'
not equal to	{<key>:{$ne:<val>}}	db.demo.find({"age":{$ne:20}}).pretty()	where age != 20

and query:

> db.demo.find({key1:val1, key2:val2}).pretty()

or query:

> db.demo.find({$or: [{key1: val1}, {key2:val2}]}).pretty()

and, or query:

> db.demo.find({"key1": "val1", $or: [{"key2": "val2"},{"key3": "val3"}]}).pretty()

$ type query

Types of	digital	Remarks
Double	1
String	2
Object	3
Array	4
Binary data	5
Undefined	6	Obsolete.
Object id	7
Boolean	8
Date	9
Null	10
Regular Expression	11
JavaScript	13
Symbol	14
JavaScript (with scope)	15
32-bit integer	16
Timestamp	17
64-bit integer	18
Min key	255	Query with -1.
Max key	127

Query the data whose name is String

db.demo.find({"name" : {$type : 2}})
或
db.demo.find({"name" : {$type : 'string'}})

> db.demo.find()
{ "_id" : ObjectId("5e79a57ba3edd4aa4ff0c2c3"), "name" : "yourName", "age" : 20, "hobby" : [ "drawing", "run" ] }
> 
> db.demo.find({"name":{$type:2}})
{ "_id" : ObjectId("5e79a57ba3edd4aa4ff0c2c3"), "name" : "yourName", "age" : 20, "hobby" : [ "drawing", "run" ] }
> 
> db.demo.find({"name":{$type:'string'}})
{ "_id" : ObjectId("5e79a57ba3edd4aa4ff0c2c3"), "name" : "yourName", "age" : 20, "hobby" : [ "drawing", "run" ] }
> 
> db.demo.find({"name":{$type:3}})
> 

limit (limit number of queries)

> db.COLLECTION_NAME.find().limit(NUMBER)

skip (number of skipped data)

> db.COLLECTION_NAME.find().limit(NUMBER).skip(NUMBER)

sort

> db.COLLECTION_NAME.find().sort({KEY:1})

> db.demo.find()
{ "_id" : ObjectId("5e79a57ba3edd4aa4ff0c2c3"), "name" : "hisName", "age" : 20, "hobby" : [ "drawing", "run" ] }
{ "_id" : ObjectId("5e79a878a3edd4aa4ff0c2c4"), "name" : "yourName", "age" : "30", "hobby" : [ "drawing", "run" ] }
> 
> db.demo.find().sort({"age":1})
{ "_id" : ObjectId("5e79a57ba3edd4aa4ff0c2c3"), "name" : "hisName", "age" : 20, "hobby" : [ "drawing", "run" ] }
{ "_id" : ObjectId("5e79a878a3edd4aa4ff0c2c4"), "name" : "yourName", "age" : "30", "hobby" : [ "drawing", "run" ] }
>
>  db.demo.find().sort({"age":-1})
{ "_id" : ObjectId("5e79a878a3edd4aa4ff0c2c4"), "name" : "yourName", "age" : "30", "hobby" : [ "drawing", "run" ] }
{ "_id" : ObjectId("5e79a57ba3edd4aa4ff0c2c3"), "name" : "hisName", "age" : 20, "hobby" : [ "drawing", "run" ] }
> 
> db.demo.find().sort({"name":-1})
{ "_id" : ObjectId("5e79a878a3edd4aa4ff0c2c4"), "name" : "yourName", "age" : "30", "hobby" : [ "drawing", "run" ] }
{ "_id" : ObjectId("5e79a57ba3edd4aa4ff0c2c3"), "name" : "hisName", "age" : 20, "hobby" : [ "drawing", "run" ] }
> 
> db.demo.find().sort({"name":1})
{ "_id" : ObjectId("5e79a57ba3edd4aa4ff0c2c3"), "name" : "hisName", "age" : 20, "hobby" : [ "drawing", "run" ] }
{ "_id" : ObjectId("5e79a878a3edd4aa4ff0c2c4"), "name" : "yourName", "age" : "30", "hobby" : [ "drawing", "run" ] }
>