How to Use SCARD Command in Redis: Count Set Members

Use the SCARD command in Redis to get the number of elements in a set stored at a given key. It returns an integer representing the set's cardinality. For example, SCARD myset returns how many members are in the set named myset.

Syntax

The SCARD command syntax is simple:

• SCARD key: Returns the number of elements in the set stored at key.
• If the key does not exist, it returns 0.
• If the key exists but is not a set, it returns an error.

redis

SCARD key

Example

This example shows how to add members to a set and then use SCARD to count them.

redis

SADD myset apple banana cherry
SCARD myset

Output

3

Common Pitfalls

Common mistakes when using SCARD include:

• Using SCARD on a key that is not a set, which causes an error.
• Expecting SCARD to return members instead of count.
• Not checking if the key exists, which returns 0 but might be mistaken for an empty set.

redis

/* Wrong: Using SCARD on a string key */
SET mykey "hello"
SCARD mykey

/* Right: Use SCARD only on set keys */
SADD myset apple
SCARD myset

Output

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

Quick Reference

Command	Description	Return Value
SCARD key	Returns the number of elements in the set at key	Integer count or 0 if key does not exist
SADD key member [member ...]	Adds one or more members to a set	Number of elements added
SMEMBERS key	Returns all members of the set	Array of members

Key Takeaways

SCARD returns the count of members in a Redis set stored at the given key.

If the key does not exist, SCARD returns 0, not an error.

Using SCARD on a non-set key causes an error.

SCARD only counts members; it does not return the members themselves.

Always ensure the key is a set before using SCARD to avoid errors.