Set key to hold string value if key does not exist. In that case, it is equal to SET. When key already holds a value, no operation is performed. SETNX is short for "SET if Not eXists".
Integer reply, specifically:1 if the key was set 0 if the key was not set
redis> SETNX mykey "Hello"(integer) 1
redis> SETNX mykey "World"(integer) 0
redis> GET mykey"Hello" redis>