SISMEMBER for membership check in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if 'user1' is a member of the set 'online_users'.

Redis

SISMEMBER online_users [1]

Drag options to blanks, or click blank then click option'

Auser1

Buser2

Cadmin

Dguest

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong member name.

Forgetting to specify the member argument.

The command SISMEMBER online_users user1 checks if 'user1' is in the set 'online_users'.

2fill in blank

medium

Complete the code to check if 'admin' is a member of the set 'user_roles'.

Redis

SISMEMBER [1] admin

Drag options to blanks, or click blank then click option'

Auser_roles

Bactive_sessions

Conline_users

Dguest_list

Attempts:

3 left

💡 Hint

Common Mistakes

Using a set name that does not contain roles.

Swapping the order of arguments.

The command SISMEMBER user_roles admin checks if 'admin' is in the set 'user_roles'.

3fill in blank

hard

Fix the error in the command to check if 'guest' is a member of 'guest_list'.

Redis

SISMEMBER guest_list [1]

Drag options to blanks, or click blank then click option'

Aguest_list

Bguest_list guest

Cguest

Dlist_guest

Attempts:

3 left

💡 Hint

Common Mistakes

Providing both set and member as one argument.

Using the set name instead of the member.

The correct command is SISMEMBER guest_list guest. The second argument must be the member name only.

4fill in blank

hard

Fill both blanks to check if 'user42' is a member of the set 'active_users'.

Redis

SISMEMBER [1] [2]

Drag options to blanks, or click blank then click option'

Aactive_users

Buser42

Cinactive_users

Duser24

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping set name and member name.

Using wrong set or member names.

The command SISMEMBER active_users user42 checks if 'user42' is in the set 'active_users'.

5fill in blank

hard

Fill all three blanks to check if 'john_doe' is a member of the set 'registered_users' and store the result in variable 'is_member'.

Redis

is_member = [1] [2] [3]

Drag options to blanks, or click blank then click option'

ASISMEMBER

Bregistered_users

Cjohn_doe

Duser_status

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong command name.

Mixing up set and member names.

Forgetting to assign the result to a variable.

The command is_member = SISMEMBER registered_users john_doe checks membership and stores the result.

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