Mongodb learning and sorting (condition operator, $type operator, limit() method, skip() method and sort() method)

One 、 Add test data

###  Insert test data 
db.wangjing_test.insert({"name":"wangjing","sex":" male ","age":27,"height":175,"weight":100});
db.wangjing_test.insert({"name":"wangjing1","sex":" male ","age":37,"height":185,"weight":110});
db.wangjing_test.insert({"name":"wangjing2","sex":" male ","age":47,"height":195,"weight":120});
db.wangjing_test.insert({"name":"wangjing3","sex":" male ","age":57,"height":205,"weight":130});

Two 、 Conditional operators

####  The conditional operator is used to compare two expressions and mongoDB Get data in collection .
### MongoDB The conditional operators in are ：
# (>)  Greater than  - $gt
# (<)  Less than  - $lt
# (>=)  Greater than or equal to  - $gte
# (<= )  Less than or equal to  - $lte

### （>=） Greater than or equal to operator  - $gte
#  Inquire about  age  Greater than or equal to  37  year 
db.wangjing_test.find({age : {$gte : 37}})

### （>） Greater than operator  - $gt
#  Query age is greater than  37  year 
db.wangjing_test.find({age : {$gt : 37}})

### MongoDB (<=)  Less than or equal to operator  - $lte
#  Query age is less than or equal to  37  year 
db.wangjing_test.find({age : {$lte : 37}})

### (<)  Less than operator  - $lt
#  The query age is less than  37  year 
db.wangjing_test.find({age : {$lt : 37}})


### MongoDB  Use  (<)  and  (>)  Inquire about  - $lt  and  $gt
#  The query age is less than 50 year , Greater than 30 year 
db.wangjing_test.find({age : {$lt : 50, $gt : 30}})

3、 ... and 、$type  The operator

#### $type Operators are based on BSON Type to retrieve the matching data types in the collection , And return the result .
###  Types that can be used in ：
#  type                          Numbers          remarks 
# Double                     1
# String                     2
# Object                     3
# Array                      4
# Binary data                5
# Undefined                  6            obsolete .
# Object id                  7
# Boolean                    8
# Date                       9
# Null                       10
# Regular Expression         11
# JavaScript                 13
# Symbol                     14
# JavaScript (with scope)    15
# 32-bit integer             16
# Timestamp                  17
# 64-bit integer             18
# Min key                    255         Query with -1.
# Max key                    127
#  Inquire about  name  Data as string 
db.wangjing_test.find({"name" : {$type : 2}})

Four 、limit（） Method

#### limit  Method to specify the number of queries ,limit() Method accepts a numeric parameter .
#  Query two pieces of data 
db.wangjing_test.find().limit(2)

5、 ... and 、skip() Method

#### skip() Method to skip a specified amount of data ,skip Method also accepts a numeric parameter as the number of records to skip .
#  Query the second data 
db.wangjing_test.find().limit(1).skip(1)

6、 ... and 、sort() Method

#### sort()  Method to sort the data ,sort()  Method can be used to specify the sorting field by parameter , And use  1  and  -1  To specify how to sort , among  1  Arrange... In ascending order , and  -1  It's for descending order .
#  Query according to age classification 
db.wangjing_test.find().sort({age:-1})

notes ： The above contents are only for reference and exchange , Do not use for commercial purposes , If there is infringement, please contact me to delete ！