Decrements the number stored at key
by one.
If the key does not exist, it is set to 0
before performing the operation.
An error is returned if the key contains a value of the wrong type or contains a
string that can not be represented as integer.
This operation is limited to 64 bit signed integers.
See INCR for extra information on increment/decrement operations.
*Return value
Integer reply: the value of key
after the decrement
*Examples
redis>
SET mykey "10"
"OK"redis> DECR mykey
(integer) 9redis> SET mykey "234293482390480948029348230948"
"OK"redis> DECR mykey
ERR ERR value is not an integer or out of range