Shulou(Shulou.com)06/01 Report--

MongoDB queries documents using the find () method.

The find () method displays all documents in an unstructured way.

The syntax format is as follows:

Db.collection.find (query, projection)

Query: optional, use the query operator to specify query conditions

Projection: optionally, use the projection operator to specify the returned key. When querying, all the key values in the document are returned, simply omitting the parameter (default omitted).

# after adding the pretty method to find, you can also display it in a format that is easier to read:

Db.tmp.find ()

{"_ id": ObjectId ("5c1757c7f4e84940e0bd578b"), "name": "aaa", "pwd": "123"," birthday ": ISODate (" 1995-09-05T00:00:00Z ")}

{"_ id": ObjectId ("5c1757f5f4e84940e0bd578c"), "name": "bbb", "pwd": "321", "birthday": ISODate ("1999-10-10T00:00:00Z")}

{"_ id": ObjectId ("5c177b84f4e84940e0bd578d"), "name": "suhaozhi", "pwd": "suhaozhi", "phone": [{"phone_num": "13333333333", "type": "cmcc"}, {"phone_num": 1555555555, "type": "chinanet"}], "type": "chinanet"}

{"_ id": ObjectId ("5c177ba1f4e84940e0bd578e"), "name": "suhaozhi", "pwd": "su", "phone": [{"phone_num": "13333333332", "type": "cmcc"}, {"phone_num": 15655555555, "type": "cnnet"}]}

{"_ id": ObjectId ("5c178a62b1d327866c98c9f7"), "x": "y"}

{"_ id": ObjectId ("5c1f226c87756129d06d2718"), "username": "aaa", "phone_num": "13333333333"}

{"_ id": ObjectId ("5c1f232587756129d06d2719"), "username": "bbb", "phone_num": ["123,456"]}

Mgset-6039947:PRIMARY > db.tmp.find (). Pretty ()

{

"_ id": ObjectId ("5c1757c7f4e84940e0bd578b")

"name": "aaa"

Pwd: 123,

Birthday: ISODate ("1995-09-05T00:00:00Z")

}

{

"_ id": ObjectId ("5c1757f5f4e84940e0bd578c")

"name": "bbb"

Pwd: 321

Birthday: ISODate ("1999-10-10T00:00:00Z")

}

{

"_ id": ObjectId ("5c177b84f4e84940e0bd578d")

"name": "suhaozhi"

"pwd": "suhaozhi"

"phone": [

{

"phone_num": "13333333333"

"type": "cmcc"

}

{

"phone_num": 155555555555

"type": "chinanet"

}

]

"type": "chinanet"

}

{

"_ id": ObjectId ("5c177ba1f4e84940e0bd578e")

"name": "suhaozhi"

"pwd": "su"

"phone": [

{

"phone_num": "13333333332"

"type": "cmcc"

}

{

"phone_num": 15655555555

"type": "cnnet"

}

]

}

{"_ id": ObjectId ("5c178a62b1d327866c98c9f7"), "x": "y"}

{

"_ id": ObjectId ("5c1f226c87756129d06d2718")

"username": "aaa"

"phone_num": "13333333333"

}

{

"_ id": ObjectId ("5c1f232587756129d06d2719")

"username": "bbb"

"phone_num": [

"123"

"456"

]

}

Query criteria:

If you are familiar with regular SQL data, you can better understand MongoDB conditional queries through the following table:

The similar statement in the operation format example RDBMS is equal to {:} db.col.find ({"by": "Rookie tutorial"}). Pretty () where by = 'Rookie tutorial' is less than {: {$lt:}} db.col.find ({"likes": {$lt:50}) .pretty () where likes

< 50小于或等于{:{$lte:}}db.col.find({"likes":{$lte:50}}).pretty()where likes 50大于或等于{:{$gte:}}db.col.find({"likes":{$gte:50}}).pretty()where likes >

= 50 is not equal to {: {$ne:}} db.col.find ({"likes": {$ne:50}}) .pretty () where likes! = 50

AND conditional query:

The find () method of MongoDB can pass in multiple keys (key), each key separated by a comma, which is the AND condition of a regular SQL.

Example:

Db.col.find ({key1:value1, key2:value2}) .pretty ()

Or conditional query:

The MongoDB OR conditional statement uses the keyword $or and the syntax format is as follows:

> db.col.find (

{

$or: [

{key1: value1}, {key2:value2}

]

}

). Pretty ()

And is used in conjunction with or:

The following example demonstrates the combined use of AND and OR, similar to the regular SQL statement: 'where age

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