Redis basic data type (hash hash)

hash

Storage type

Store multiple unordered key-value pairs, the maximum storage amount is 2^32-1 (about 4 billion), value can only be a string, and other types cannot be nested

Advantages and disadvantages with String

1. advantage
   • Gather all relevant values ​​into one key to save memory space
   • Use only one key to reduce key conflicts
   • When you need to get values ​​in batches, you only need to use one command to reduce memory/IO/CPU consumption
2. Disadvantage
   • Field cannot set expiration time separately
   • Need to consider the distribution of data volume (when there are a lot of fields, it cannot be distributed to multiple nodes)

Common operation commands

hset: set value

• command

  HSET key field value
  

• Description

  Set the value of the specified field in the hash set specified by key.

  If the hash set specified by the key does not exist, a new hash set will be created and associated with the key.

  If the field exists in the hash set, it will be overwritten.

• return value

  • 1-if field is a new field
  • 0-If the field originally existed in the map

• example

  redis> HSET myhash field1 "Hello"
  (integer) 1
  redis> HGET myhash field1
  "Hello"
  redis> 
  

hget: Get the value

• command

  HGET key field
  

• Description

  Returns the value associated with the field in the hash set specified by key

• return value

  The value associated with this field. When the field does not exist or the key does not exist, nil is returned.

• example

  redis> HSET myhash field1 "foo"
  (integer) 1
  redis> HGET myhash field1
  "foo"
  redis> HGET myhash field2
  (nil)
  redis> 
  

hmset: set multiple values

• command

  HMSET key field value [field value ...]
  

• Description

  Set the keyvalue of the specified concentration of the specified field hashes. This command will rewrite all the fields that exist in the hash set. If the keyspecified hash set does not exist, create a new hash set and the keyassociated

• example

  redis> HMSET myhash field1 "Hello" field2 "World"
  OK
  redis> HGET myhash field1
  "Hello"
  redis> HGET myhash field2
  "World"
  redis> 
  

hmget: Get multiple values

• command

  HMGET key field [field ...]
  

• Description

  Returns the keyvalue of the specified concentration of the specified field hashes.

  For each hash focused field does not exist, the return nilvalue. Because they do not exist keys is considered to be an empty hash set to a non-existent keyexecution HMGETwill return only contain a nillist of values

• return value

  Contains a list of the given fields and their values, and keeps the same order as the request.

• example

  redis> HSET myhash field1 "Hello"
  (integer) 1
  redis> HSET myhash field2 "World"
  (integer) 1
  redis> HMGET myhash field1 field2 nofield
  1) "Hello"
  2) "World"
  3) (nil)
  redis> 
  

hkeys: Get all the key values ​​of the hash

• command

  HKEYS key
  

• Description

  Returns the names of all fields in the hash set specified by key.

• return value

  The list of fields in the hash set, an empty list is returned when the hash set specified by key does not exist.

• example

  redis> HSET myhash field1 "Hello"
  (integer) 1
  redis> HSET myhash field2 "World"
  (integer) 1
  redis> HKEYS myhash
  1) "field1"
  2) "field2"
  redis> 
  

hvals: get all value values ​​of key

• command

  HVALS key
  

• Description

  Returns the values ​​of all fields in the hash set specified by key.

• return value

  A list of values ​​in the hash set. When the hash set specified by key does not exist, an empty list is returned.

• example

  redis> HSET myhash field1 "Hello"
  (integer) 1
  redis> HSET myhash field2 "World"
  (integer) 1
  redis> HVALS myhash
  1) "Hello"
  2) "World"
  redis> 
  

hgetall: Get all the field and value values ​​of the key

• command

  HGETALL key
  

• Description

  Returns all the fields and values ​​in the hash set specified by key. In the return value, the next of each field name is its value, so the length of the return value is twice the size of the hash set

• return value

  A list of fields and values ​​in the hash set. When the hash set specified by key does not exist, an empty list is returned.

• example

  redis> HSET myhash field1 "Hello"
  (integer) 1
  redis> HSET myhash field2 "World"
  (integer) 1
  redis> HGETALL myhash
  1) "field1"
  2) "Hello"
  3) "field2"
  4) "World"
  redis> 
  

hdel: delete the field specified in the key

• command

  HDEL key field [field ...]
  

• Description

  Remove the specified domain from the hash set specified by key. Domains that do not exist in the hash set will be ignored.

  If the hash set specified by key does not exist, it will be regarded as an empty hash set, and the command will return 0.

• return value

  Returns the number of domains successfully removed from the hash set, excluding those domains that are indicated but do not exist

• example

  redis> HSET myhash field1 "foo"
  (integer) 1
  redis> HDEL myhash field1
  (integer) 1
  redis> HDEL myhash field2
  (integer) 0
  redis> 
  

hlen: Get the number of fields contained in the hash

• command

  HLEN key
  

• Description

  Returns keythe number of fields included in the hash set specified.

• return value

  The number of fields in the hash, as key0 if the specified hash set does not exist

• example

  redis> HSET myhash field1 "Hello"
  (integer) 1
  redis> HSET myhash field2 "World"
  (integer) 1
  redis> HLEN myhash
  (integer) 2
  redis> 
  

hexists: Determine whether the hash exists

• command

  HEXISTS key field
  

• Description

  Returns whether the field exists in the hash

• return value

  • 1 --hash contains the field.
  • 0 --hash does not contain the field or the key does not exist.

• example

  redis> HSET myhash field1 "foo"
  (integer) 1
  redis> HEXISTS myhash field1
  (integer) 1
  redis> HEXISTS myhash field2
  (integer) 0
  redis> 
  

hincrby: the integer value in the hash increases

• command

  HINCRBY key field increment
  

• Description

  Increase keyspecified hash centralized specified numeric fields. If keydoes not exist, create a new hash set and with the keyassociation. If the field does not exist, the value of the field is set to 0 before the operation is performed

  HINCRBY The range of supported values ​​is limited to 64-bit signed integers

• return value

  The value of this field after the value-added operation is executed.

• example

  redis> HSET myhash field 5
  (integer) 1
  redis> HINCRBY myhash field 1
  (integer) 6
  redis> HINCRBY myhash field -1
  (integer) 5
  redis> HINCRBY myhash field -10
  (integer) -5
  redis> 
  

hincrbyfloat: Increase in floating point number in hash

• command

  HINCRBYFLOAT key field increment
  

• Description

  Perform a float type addition for the specified keyhash fieldfield value increment. If it fielddoes not exist, set it to 0 before performing the operation. If one of the following situations occurs, an error is returned:

  • fieldThe value contains the wrong type (not a string).
  • Currently fieldor incrementcannot be parsed as a float type.

• return value

  fieldImplementation of incrementvalue added

• example

  redis> HSET mykey field 10.50
  (integer) 1
  redis> HINCRBYFLOAT mykey field 0.1
  "10.6"
  redis> HSET mykey field 5.0e3
  (integer) 0
  redis> HINCRBYFLOAT mykey field 2.0e2
  "5200"
  redis> 
  

hsetnx

• command

  HSETNX key field value
  

• Description

  Only keywhen the specified hash concentration specified field does not exist, setting the value of the field. If the keyspecified hash set does not exist, create a new hash set and with the keyassociation. If the field already exists, this operation has no effect.

• return value

  • 1-If the field is a new field and successfully assigned
  • 0-If the field already exists in the hash set, no operation is performed

• example

  redis> HSETNX myhash field "Hello"
  (integer) 1
  redis> HSETNX myhash field "World"
  (integer) 0
  redis> HGET myhash field
  "Hello"
  redis> 
  

hstrlen: Get the string length of the value of the hash specified field

• command

  HSTRLEN key field
  

• return value

  Returns the string length of the value of the hash specified field. If the hash or field does not exist, return 0.

• example

  redis> HMSET myhash f1 HelloWorld f2 99 f3 -256
  OK
  redis> HSTRLEN myhash f1
  (integer) 10
  redis> HSTRLEN myhash f2
  (integer) 2
  redis> HSTRLEN myhash f3
  (integer) 4
  redis>