SCARD for set size in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Redis command SCARD do?

The SCARD command returns the number of elements in a set stored at a given key.

beginner

How do you use SCARD to find the size of a set named myset?

You run SCARD myset. This returns the count of elements in the set myset.

beginner

What will SCARD return if the set does not exist?

It returns 0 because a non-existing set is considered empty.

intermediate

Can SCARD be used on data types other than sets?

No, SCARD only works on sets. Using it on other types will cause an error.

beginner

Why is SCARD useful in real life?

It helps quickly find how many unique items are in a group, like counting unique visitors or tags.

What does the Redis command SCARD myset return?

A Adds an element to the set <code>myset</code>

B All elements in the set <code>myset</code>

C Removes the set <code>myset</code>

D Number of elements in the set <code>myset</code>

SCARD returns the count of elements in the specified set.

If the set users does not exist, what does SCARD users return?

A 0

B An error

C null

D 1

SCARD returns 0 for non-existing sets because they are empty.

Which data type does SCARD work with?

A Strings

B Sets

C Hashes

D Lists

SCARD is designed to work only with sets.

What happens if you run SCARD on a key holding a string?

A Returns the string length

B Returns 0

C Throws an error

D Converts string to set and returns size

Using SCARD on non-set types causes a type error in Redis.

Why might you use SCARD in a web app?

A To count unique visitors stored in a set

B To delete user data

C To add new users

D To sort user names

SCARD helps count unique items like visitors efficiently.

Explain what the Redis command SCARD does and give a simple example.

Think about counting unique items in a group.

Describe what happens if you use SCARD on a key that is not a set.

Consider Redis data types and command compatibility.