redis zadd NX CH #7
Description
XX: Only update elements that already exist. Never add elements.
NX: Don't update already existing elements. Always add new elements.
CH: Modify the return value from the number of new elements added, to the total number of elements changed (CH is an abbreviation of changed). Changed elements are new elements added and elements already existing for which the score was updated. So elements specified in the command line having the same score as they had in the past are not counted. Note: normally the return value of ZADD only counts the number of new elements added.