In Redis, the SUNION command returns the members of the set resulting from the union of all of the given sets.

Syntax

The syntax goes like this:

SUNION key [key ...]

We can pass one or more keys to the command.

Example

Suppose we create the following sets:

SADD cats Fluffy Scratch Meow
SADD dogs Wag Bark Fluffy

We can use SUNION to return the union of those two sets:

SUNION cats dogs

Result:

1) "Bark"
2) "Scratch"
3) "Fluffy"
4) "Meow"
5) "Wag"

Note that duplicate values are only included once. This makes sense, because sets can only contain unique values, and the result of SUNION is a set. In our example, Fluffy appears in both the cats and dogs sets, but it only appears once in the set resulting from SUNION.

Non-Existent Sets

Sets that don’t exist are treated as empty sets:

SUNION cats dogs elephants

Result:

1) "Bark"
2) "Scratch"
3) "Fluffy"
4) "Meow"
5) "Wag"

Here, we added a third set called elephants, but that set doesn’t exist. The result is the same as the previous example.

Union of a Single Set

If we pass a single set, we simply get the members of that set:

SUNION cats

Result:

1) "Meow"
2) "Scratch"
3) "Fluffy"

Wrong Argument Count

Calling SUNION without any arguments results in an error:

SUNION

Result:

(error) ERR wrong number of arguments for 'sunion' command