SISMEMBER for membership check in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Check if a member exists in a Redis set

Given a Redis set named fruits containing apple, banana, and cherry, what is the output of SISMEMBER fruits banana?

Redis

SISMEMBER fruits banana

A 0

B 1

C nil

D error

💡 Hint

SISMEMBER returns 1 if the element is in the set, otherwise 0.

The command SISMEMBER fruits banana checks if banana is a member of the set fruits. Since banana is in the set, it returns 1.

❓ query_result

intermediate

Check membership of a non-existing element

What is the output of SISMEMBER fruits orange if the set fruits contains apple, banana, and cherry?

Redis

SISMEMBER fruits orange

A 1

B error

C nil

D 0

💡 Hint

SISMEMBER returns 0 if the element is not in the set.

The command SISMEMBER fruits orange checks if orange is in the set fruits. Since it is not, the command returns 0.

📝 Syntax

advanced

Identify the syntax error in SISMEMBER usage

Which option shows an incorrect syntax for the SISMEMBER command?

A SISMEMBER fruits

B SISMEMBER fruits cherry

C SISMEMBER fruits orange

D SISMEMBER fruits banana

💡 Hint

SISMEMBER requires exactly two arguments: the set key and the member to check.

Option A is missing the member argument. The correct syntax is SISMEMBER <key> <member>. Without the member, Redis returns a syntax error.

❓ query_result

advanced

Check membership on a non-existing set

What is the output of SISMEMBER colors red if the set colors does not exist in Redis?

Redis

SISMEMBER colors red

A 1

B nil

C 0

D error

💡 Hint

SISMEMBER returns 0 if the set does not exist.

If the set colors does not exist, Redis treats it as an empty set. Checking membership returns 0 because red is not a member.

🧠 Conceptual

expert

Understanding SISMEMBER return values

Which statement correctly describes the return values of the Redis SISMEMBER command?

A Returns 1 if the member exists, 0 if not, and 0 if the set does not exist

B Returns true if the member exists, false if not, and error if the set does not exist

C Returns 1 if the member exists in the set, 0 if not, and nil if the set does not exist

D Returns the member value if it exists, otherwise returns nil

💡 Hint

Think about how Redis treats non-existing sets for membership checks.

The SISMEMBER command returns 1 if the member is in the set, 0 if the member is not in the set, and also 0 if the set does not exist (treated as empty). It never returns nil or errors for non-existing sets.

Practice

1. What does the Redis command SISMEMBER do?

easy

A. Adds a value to a set

B. Removes a value from a set

C. Checks if a value is a member of a set and returns 1 or 0

D. Returns all members of a set

Solution

1. Step 1: Understand SISMEMBER purpose

   The SISMEMBER command checks membership of a value in a Redis set.

2. Step 2: Identify return values

   It returns 1 if the value is in the set, otherwise 0.

3. Final Answer:

   Checks if a value is a member of a set and returns 1 or 0 -> Option C

4. Quick Check:

   SISMEMBER returns 1 or 0 [OK]

Hint: SISMEMBER returns 1 if present, else 0 [OK]

Common Mistakes:

• Confusing SISMEMBER with SADD or SREM
• Expecting SISMEMBER to return the value itself
• Thinking SISMEMBER returns all set members

2. Which of the following is the correct syntax to check if 'apple' is in the set 'fruits' using Redis?

easy

A. SISMEMBER(fruits, apple)

B. SISMEMBER 'fruits' 'apple'

C. SISMEMBER fruits, apple

D. SISMEMBER fruits apple

Solution

1. Step 1: Recall Redis command syntax

   Redis commands use space-separated arguments without commas or parentheses.

2. Step 2: Match correct syntax

   Correct syntax is SISMEMBER key member, so SISMEMBER fruits apple is correct.

3. Final Answer:

   SISMEMBER fruits apple -> Option D

4. Quick Check:

   Redis commands use spaces, no commas or quotes needed [OK]

Hint: Use space-separated arguments without quotes or commas [OK]

Common Mistakes:

• Adding commas between arguments
• Using parentheses like a function call
• Adding quotes around arguments unnecessarily

3. Given the Redis set 'colors' contains {"red", "blue", "green"}, what is the output of SISMEMBER colors yellow?

medium

A. 0

B. 1

C. red

D. Error

Solution

1. Step 1: Check if 'yellow' is in the set 'colors'

   The set contains "red", "blue", and "green" but not "yellow".

2. Step 2: Understand SISMEMBER return value

   SISMEMBER returns 1 if member exists, else 0. Since "yellow" is not in the set, it returns 0.

3. Final Answer:

   0 -> Option A

4. Quick Check:

   Member absent = 0 [OK]

Hint: If value not in set, SISMEMBER returns 0 [OK]

Common Mistakes:

• Assuming it returns the value itself
• Confusing 0 with an error
• Thinking it returns the whole set

4. You run the command SISMEMBER colors without specifying a member. What will happen?

medium

A. Syntax error

B. Returns 1

C. Returns 0

D. Returns all members

Solution

1. Step 1: Check command argument requirements

   SISMEMBER requires exactly two arguments: the set key and the member to check.

2. Step 2: Analyze missing argument effect

   Omitting the member argument causes a syntax error in Redis.

3. Final Answer:

   Syntax error -> Option A

4. Quick Check:

   Missing arguments cause syntax error [OK]

Hint: SISMEMBER needs two arguments; missing one causes error [OK]

Common Mistakes:

• Expecting default member to be checked
• Thinking it returns 0 if member missing
• Assuming it returns all members

5. You have a Redis set 'users' with members {"alice", "bob", "carol"}. You want to check if 'dave' is a member and add him only if he is not already present. Which sequence of commands correctly does this?

hard

A. SISMEMBER users dave
SREM users dave

B. SISMEMBER users dave
SADD users dave

C. SADD users dave
SISMEMBER users dave

D. SREM users dave
SADD users dave

Solution

1. Step 1: Check membership before adding

   Use SISMEMBER to see if 'dave' is already in 'users'.

2. Step 2: Add 'dave' only if not present

   If SISMEMBER returns 0, then use SADD to add 'dave'.

3. Final Answer:

   SISMEMBER users dave SADD users dave -> Option B

4. Quick Check:

   Check membership then add if absent [OK]

Hint: Check with SISMEMBER before SADD to avoid duplicates [OK]

Common Mistakes:

• Adding before checking membership
• Removing member instead of adding
• Checking membership after adding