ZADD

Synopsis

ZADD key [NX|XX] [CH] [INCR] score member [score member ...]

This command sets all specified members with their respective scores in the sorted set specified by key, with multiple score member pairs possible. If a specified member is already in the sorted set, this command updates that member with the new score. If the key does not exist, a new sorted set is created, with the specified pairs as the only elements in the set. A score should be a double, while a member can be any string.

Return value

The number of new members added to the sorted set, unless the CH option is specified (see below).

ZADD options

  • XX: Only update members that already exist. Do not add new members.
  • NX: Do not update members that already exist. Only addd new members.
  • CH: Modify the return value from new members added to members added or updated.
  • INCR: Increment the specified member by score. Only one score member pair can be specified.

Examples

Add two elements into the sorted set.

$ ZADD z_key 1.0 v1 2.0 v2

(integer) 2

Update an element in the set. Note the return value is 0, since you do not add a new member.

$ ZADD z_key 3.0 v1

(integer) 0

Now you add a new member with an existing score. This is fine, since multiple members can have the same score.

$ ZADD z_key 3.0 v3

(integer) 1

Now, see the members in the sorted set. Note the sort order by score. Since both v1 and v3 have the same score, you use comparison on the members themselves to determine order.

$ ZRANGEBYSCORE z_key -inf +inf WITHSCORES

1) "v2"
2) "2.0"
3) "v1"
4) "3.0"
5) "v3"
6) "3.0"

With the XX option specified, only update exiting members. Here, only v1 is modified.

$ ZADD z_key XX 1.0 v1 4.0 v4

(integer) 0

With the NX option specified, only add new members. Here only v4 is added.

$ ZADD z_key NX 0.0 v1 4.0 v4

(integer) 1

With the CH option specified, return number of new and updated members.

$ ZADD z_key CH 0.0 v1 5.0 v5

(integer) 2

With the INCR option specified, increment by score. Score of v5 should now be 6.0.

$ ZADD z_key INCR 1.0 v5

Let us now see the updated sorted set.

$ ZRANGEBYSCORE z_key -inf +inf

1) "v1"
2) "0.0"
3) "v2"
4) "2.0"
5) "v3"
6) "3.0"
7) "v4"
8) "4.0"
9) "v5"
10) "6.0"

See also

zcard, zrange, zrangebyscore, zrem, zrevrange