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ZUNION

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ZUNION numkeys key [key ...] [WEIGHTS weight [weight ...]] [AGGREGATE SUM | MIN | MAX] [WITHSCORES]
Group
Sorted set
Complexity
O(N)+O(M*log(M)) where N is the total size of the input sets and M is the size of the result
Arity
-3 (at least 3 words, counting the command name)
Flags
read-only
HotKV Cloud
All plans
On-Premise
no license needed

ZUNION returns every member that appears in at least one of the given sorted sets, ordered by its combined score. A member’s combined score is built from its score in each input that contains it, by default by adding them up.

Inputs can also be plain sets; their members count as having score 1. Missing keys count as empty. To store the result instead, use ZUNIONSTORE.

Options

Section titled “Options”
Option Effect
numkeys How many keys follow. Must be at least 1.
WEIGHTS weight ... One multiplier per input key, applied to that input’s scores before they are combined. Default 1 each.
AGGREGATE SUM Add up the (weighted) scores. The default.
AGGREGATE MIN Keep the lowest (weighted) score.
AGGREGATE MAX Keep the highest (weighted) score.
WITHSCORES Return each member with its combined score. Must be the last argument.

Return value

Section titled “Return value”
Case RESP2 RESP3
Success Array of members Same
With WITHSCORES Flat array: member, score, … (scores as bulk strings) Array of [member, score] pairs, the score a double

Errors:

  • ERR value is not an integer or out of range if numkeys is not an integer, and ERR at least 1 input key is needed for 'zunion' command if it is below 1.
  • ERR syntax error if fewer keys follow than numkeys says, WEIGHTS has too few values, the AGGREGATE value is unknown, or anything else follows.
  • ERR weight value is not a float for a weight that is not a number.
  • WRONGTYPE if a key holds something other than a sorted set or a set. Key types are checked before the options.

Examples

Section titled “Examples”
127.0.0.1:6379> ZADD q1 10 "alice" 5 "bob"
(integer) 2
127.0.0.1:6379> ZADD q2 3 "bob" 7 "carol"
(integer) 2
127.0.0.1:6379> ZUNION 2 q1 q2 WITHSCORES
1) "carol"
2) "7"
3) "bob"
4) "8"
5) "alice"
6) "10"
127.0.0.1:6379> ZUNION 2 q1 q2 WEIGHTS 1 2 AGGREGATE MAX
1) "bob"
2) "alice"
3) "carol"

Compatibility

Section titled “Compatibility”

Same replies as Redis 7.4 and Valkey 8. HotKV requires WITHSCORES to be the last argument; Redis and Valkey also accept it before WEIGHTS or AGGREGATE.

See also

Section titled “See also”

ZUNIONSTORE, ZINTER, ZDIFF, SUNION