How to Use ZCARD in Redis: Syntax and Examples

Use the ZCARD command in Redis to get the number of elements in a sorted set. The command takes the key of the sorted set and returns an integer count of its members.

Syntax

The ZCARD command syntax is simple:

• ZCARD key: Returns the number of elements in the sorted set stored at key.

If the key does not exist, it returns 0.

redis

ZCARD mySortedSet

Example

This example shows how to add elements to a sorted set and then use ZCARD to count them.

redis

127.0.0.1:6379> ZADD mySortedSet 1 "apple" 2 "banana" 3 "cherry"
(integer) 3
127.0.0.1:6379> ZCARD mySortedSet
(integer) 3

Output

(integer) 3

Common Pitfalls

Common mistakes when using ZCARD include:

• Using ZCARD on a key that is not a sorted set, which returns an error.
• Expecting ZCARD to return the count of elements in other data types like sets or lists.
• Not handling the case when the key does not exist, which returns 0.

redis

127.0.0.1:6379> SET myKey "value"
OK
127.0.0.1:6379> ZCARD myKey
(error) WRONGTYPE Operation against a key holding the wrong kind of value

-- Correct usage --
127.0.0.1:6379> ZADD mySortedSet 1 "one"
(integer) 1
127.0.0.1:6379> ZCARD mySortedSet
(integer) 1

Output

(error) WRONGTYPE Operation against a key holding the wrong kind of value
(integer) 1

Quick Reference

Command	Description
ZCARD key	Returns the number of elements in the sorted set at key
Returns 0 if key does not exist	No error, just zero count
Error if key is not a sorted set	Wrong type error returned

Key Takeaways

ZCARD returns the count of elements in a sorted set by key.

If the key does not exist, ZCARD returns 0 without error.

Using ZCARD on a non-sorted set key causes a type error.

ZCARD only works with sorted sets, not other Redis data types.