SADD and SREM for membership in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Redis command SADD do?

The SADD command adds one or more members to a set stored at a key. If the members are already in the set, they are ignored.

beginner

What happens if you use SREM on a member that is not in the set?

If the member is not in the set, SREM does nothing and returns 0, meaning no members were removed.

intermediate

How can you check if a member exists in a Redis set?

Use the SISMEMBER command. It returns 1 if the member exists in the set, otherwise 0.

beginner

Can SADD add multiple members at once? How?

Yes, SADD can add multiple members by listing them all after the key, separated by spaces.

intermediate

What is the return value of SADD?

SADD returns the number of members that were actually added to the set, excluding those already present.

What does the Redis command SREM myset member1 do?

A Adds 'member1' to the set 'myset'

B Deletes the entire set 'myset'

C Checks if 'member1' is in 'myset'

D Removes 'member1' from the set 'myset' if it exists

SREM removes specified members from a set if they exist.

If you run SADD myset a b c and 'a' and 'b' are already in 'myset', what does it return?

A 0

B 3

C 1

D 2

SADD returns the count of new members added. Only 'c' is new here.

Which command checks if a member is in a Redis set?

A SISMEMBER

B SREM

C SADD

D SMEMBERS

SISMEMBER returns 1 if the member exists, 0 otherwise.

What does SREM myset x y return if only 'x' is in 'myset'?

A 2

B 1

C 0

D Error

SREM returns the number of members removed. Only 'x' was removed.

Can SADD add duplicate members to a set?

A No, duplicates are ignored

B Yes, duplicates are added

C Only if you use a special flag

D It depends on the Redis version

Sets do not allow duplicates; SADD ignores members already present.

Explain how SADD and SREM work for managing membership in Redis sets.

Think about adding and removing friends from a group.

Describe how you would check if a member exists in a Redis set and then remove it if present.

First check, then remove if found.