SADD and SREM for membership in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the result of adding members with SADD?

You have an empty Redis set named fruits. You run the command SADD fruits apple banana apple. What is the return value of this command?

Redis

SADD fruits apple banana apple

A 3

B 2

C 1

D 0

💡 Hint

SADD adds only unique members and returns the number of new elements added.

The command adds 'apple' and 'banana' to the set. 'apple' is repeated but only counted once. So 2 new members are added.

❓ query_result

intermediate

What happens when removing members with SREM?

Given a Redis set colors containing {red, green, blue}, what does the command SREM colors green yellow return?

Redis

SREM colors green yellow

A 3

B 2

C 0

D 1

💡 Hint

SREM returns the number of members actually removed from the set.

Only 'green' exists in the set and is removed. 'yellow' does not exist, so only 1 member is removed.

📝 Syntax

advanced

Which SADD command is syntactically correct?

Choose the correct syntax to add multiple members to a Redis set named pets:

A SADD pets [dog cat bird]

B SADD pets (dog, cat, bird)

C SADD pets dog cat bird

D SADD pets 'dog', 'cat', 'bird'

💡 Hint

Redis commands list members separated by spaces without brackets or quotes.

Option C uses the correct syntax: command name, key, then members separated by spaces.

❓ query_result

advanced

What is the set content after SADD and SREM commands?

Starting with an empty set numbers, you run these commands in order:
1. SADD numbers 1 2 3 4
2. SREM numbers 2 5
3. SADD numbers 5 6
What members does the set numbers contain now?

Redis

SADD numbers 1 2 3 4
SREM numbers 2 5
SADD numbers 5 6

A {1, 3, 4, 5, 6}

B {1, 2, 3, 4, 5, 6}

C {1, 3, 4, 6}

D {2, 3, 4, 5, 6}

💡 Hint

Remember SREM removes only existing members; SADD adds unique members.

After first SADD: {1,2,3,4}. SREM removes 2 (exists) and 5 (does not exist), so set is {1,3,4}. Then SADD adds 5 and 6, final set is {1,3,4,5,6}.

🧠 Conceptual

expert

Why does SADD return 0 sometimes?

You run SADD animals dog cat on a set that already contains {dog, cat}. What does the return value 0 mean in this context?

A No new members were added because all were already present

B The command failed due to a syntax error

C The set was deleted before the command ran

D The command added zero members because the set is full

💡 Hint

SADD returns the count of new unique members added, not total members.

If all members are already in the set, SADD returns 0 indicating no new additions.