DECR

The DECR command in DiceDB is used to decrement the integer value of a key by one. If the key does not exist, it is set to 0 before performing the decrement operation. This command is useful for counters and other numerical operations where you need to decrease the value stored at a specific key.

Syntax

DECR key

Parameters

Parameter	Description	Type	Required
key	The key whose value you want to decrement. This key must hold a string that can be represented as an integer.	String	Yes

Return Value

Condition	Return Value
Command is successful	Integer: The new value of the key after the decrement operation.
Syntax or specified constraints are invalid	error

Behaviour

When the DECR command is executed, the following steps occur:

• If the specified key doesn’t exist, it is created, with -1 as it’s value, and same is returned.
• If the specified key exists with an integer value, value is decremented and new value is returned.
• If the specified key exists with a non-integer OR out-of-range value, error message is returned as:
  • (error) ERR value is not an integer or out of range

Errors

The DECR command can raise errors in the following scenarios:

1. Wrong Type Error: If the key exists but the value is not a string that can be represented as an integer, DiceDB will return an error.
   • Error Message: (error) ERR value is not an integer or out of range
2. Out of Range Error: If the value of the key is out of the range of a 64-bit signed integer after the decrement operation, DiceDB will return an error.
   • Error Message: (error) ERR increment or decrement would overflow

Example Usage

Basic Usage

127.0.0.1:7379> SET mycounter 10
OK
127.0.0.1:7379> DECR mycounter
9

Explanation:

1. The SET command initializes the key mycounter with the value 10.
2. The DECR command decrements the value of mycounter by 1, resulting in 9.

Key Does Not Exist

127.0.0.1:7379> DECR newcounter
(integer) -1

Explanation:

1. The key newcounter does not exist.
2. DiceDB sets newcounter to 0 and then decrements it by 1, resulting in -1.

Error Scenario: Non-Integer Value

127.0.0.1:7379> SET mystring "hello"
OK
127.0.0.1:7379> DECR mystring
(error) ERR value is not an integer or out of range

Explanation:

1. The SET command initializes the key mystring with the value "hello".
2. The DECR command attempts to decrement the value of mystring, but since it is not an integer, an error is raised.

Error Scenario: Out of Range

127.0.0.1:7379> SET mycounter 234293482390480948029348230948
OK
127.0.0.1:7379> DECR mycounter
(error) ERR value is not an integer or out of range

Explanation:

1. The SET command initializes the key mycounter with the out-of-range value for a 64-bit signed integer.
2. The DECR command attempts to decrement the value of mycounter, but this would result in an overflow, so an error is raised.

Alternatives

You can also use the DECRBY command to decrement the value of a key by a specified amount.