SISMEMBER for membership check in Redis - Step-by-Step Execution

Concept Flow - SISMEMBER for membership check

Start

↓

Check if element exists in set

Yes No↓

Return 1

↓

End

SISMEMBER checks if a given element is in a Redis set and returns 1 if yes, 0 if no.

Execution Sample

Redis

SADD fruits apple banana cherry
SISMEMBER fruits banana
SISMEMBER fruits orange

Add three fruits to a set, then check if 'banana' and 'orange' are members.

Execution Table

Step	Command	Set Content	Element Checked	Result	Explanation
1	SADD fruits apple banana cherry	apple, banana, cherry	-	-	Add elements to set 'fruits'
2	SISMEMBER fruits banana	apple, banana, cherry	banana	1	'banana' is in the set, returns 1
3	SISMEMBER fruits orange	apple, banana, cherry	orange	0	'orange' not in set, returns 0

💡 All commands executed; membership checks returned 1 or 0 accordingly.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3
fruits set	empty	apple, banana, cherry	apple, banana, cherry	apple, banana, cherry
SISMEMBER result	N/A	N/A	1	0

Key Moments - 2 Insights

Why does SISMEMBER return 1 for 'banana' but 0 for 'orange'?

Because 'banana' was added to the set in step 1 (see execution_table row 1), so SISMEMBER finds it and returns 1. 'orange' was never added, so it returns 0 (see row 3).

Does SISMEMBER change the set contents?

No, SISMEMBER only checks membership and does not modify the set. The set remains the same after membership checks (see variable_tracker for 'fruits set').

Visual Quiz - 3 Questions

Look at the execution_table, what is the result of SISMEMBER checking 'banana'?

A -1

B 0

C 1

D Error

💡 Hint

Check execution_table row 2 under 'Result' column.

At which step does the set 'fruits' get its elements added?

A Step 2

B Step 1

C Step 3

D No step adds elements

💡 Hint

Look at execution_table row 1 where SADD command is executed.

If we check SISMEMBER for 'apple' after step 3, what would the result be?

A 1

B 0

C Error

D Depends on previous commands

💡 Hint

Refer to variable_tracker showing 'apple' is in the set after step 1 and no changes after.

Concept Snapshot

SISMEMBER key element
- Checks if 'element' is in the set stored at 'key'
- Returns 1 if present, 0 if not
- Does not modify the set
- Useful for quick membership tests in Redis sets

Full Transcript

This visual execution shows how the Redis command SISMEMBER works. First, elements 'apple', 'banana', and 'cherry' are added to the set 'fruits' using SADD. Then, SISMEMBER checks if 'banana' is in the set and returns 1 because it is present. Next, it checks for 'orange' and returns 0 because 'orange' was never added. The set remains unchanged during membership checks. This helps understand how SISMEMBER quickly tells if an element is part of a Redis set without changing data.