SADD and SREM for membership in Redis - Step-by-Step Execution

Concept Flow - SADD and SREM for membership

Start with empty set

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SADD adds members

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Check membership with SISMEMBER

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SREM removes members

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Check membership again

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End with updated set

This flow shows how we add members to a set, check if they exist, remove some, and check membership again.

Execution Sample

Redis

SADD myset apple banana cherry
SISMEMBER myset banana
SREM myset banana
SISMEMBER myset banana

Add three fruits to a set, check if banana is in it, remove banana, then check membership again.

Execution Table

Step	Command	Action	Result	Set State
1	SADD myset apple banana cherry	Add members apple, banana, cherry	3 (added count)	{apple, banana, cherry}
2	SISMEMBER myset banana	Check if banana is member	1 (yes)	{apple, banana, cherry}
3	SREM myset banana	Remove banana from set	1 (removed count)	{apple, cherry}
4	SISMEMBER myset banana	Check if banana is member	0 (no)	{apple, cherry}

💡 All commands executed; membership updated accordingly.

Variable Tracker

Variable	Start	After Step 1	After Step 3	Final
myset	{}	{apple, banana, cherry}	{apple, cherry}	{apple, cherry}

Key Moments - 2 Insights

Why does SISMEMBER return 1 before removal and 0 after?

Because before removal (Step 2), banana is in the set (Step 1 added it). After removal (Step 4), banana is no longer in the set (Step 3 removed it).

What does the number returned by SADD and SREM mean?

SADD returns how many new members were added (Step 1 returns 3). SREM returns how many members were removed (Step 3 returns 1).

Visual Quiz - 3 Questions

Look at the execution table, what is the set after Step 1?

A {apple, cherry}

B {banana, cherry}

C {apple, banana, cherry}

D {}

💡 Hint

Check the 'Set State' column in Step 1.

At which step does banana get removed from the set?

A Step 2

B Step 3

C Step 4

D Banana is never removed

💡 Hint

Look at the 'Command' and 'Action' columns to find when SREM is called.

If we add 'banana' again after Step 3, what would SADD return?

A 1

B 0

C 2

D Error

💡 Hint

SADD returns how many new members were added; banana was removed before, so adding it again counts as 1.

Concept Snapshot

SADD key member [member ...] - Adds members to a set, returns count added
SREM key member [member ...] - Removes members, returns count removed
SISMEMBER key member - Checks if member exists, returns 1 or 0
Use SADD to add, SREM to remove, SISMEMBER to check membership.

Full Transcript

This example shows how Redis set commands SADD and SREM work for membership management. We start with an empty set 'myset'. Using SADD, we add three members: apple, banana, and cherry. The command returns 3, meaning all three were added. Next, SISMEMBER checks if banana is in the set and returns 1 (true). Then, SREM removes banana and returns 1, indicating one member removed. Finally, SISMEMBER checks banana again and returns 0 (false), confirming banana is no longer in the set. The set changes from empty to {apple, banana, cherry}, then to {apple, cherry} after removal. This shows how to add, check, and remove members in Redis sets.