ZSCORE for member score in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the score of a member from a sorted set.

Redis

ZSCORE [1] member1

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

AZRANGE

BZADD

Cmyset

Dmember1

Attempts:

3 left

💡 Hint

Common Mistakes

Using the member name as the sorted set key.

Using commands like ZADD or ZRANGE instead of the sorted set key.

The command ZSCORE myset member1 returns the score of member1 in the sorted set myset.

2fill in blank

medium

Complete the code to get the score of 'player42' from the sorted set 'game_scores'.

Redis

ZSCORE [1] player42

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

Agame_scores

Bplayer42

Cscores

Dplayers

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing the member name with the sorted set key.

Using a wrong sorted set key.

The command ZSCORE game_scores player42 fetches the score of player42 from the sorted set game_scores.

3fill in blank

hard

Fix the error in the command to get the score of 'user99' from 'leaderboard'.

Redis

ZSCORE leaderboard [1]

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

Auser99

Bleaderboard

Cuser100

Dscore

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong member name.

Using the sorted set name as the member.

The member name must be user99 to get the correct score from the leaderboard sorted set.

4fill in blank

hard

Fill both blanks to get the score of 'memberX' from the sorted set 'scores_set'.

Redis

ZSCORE [1] [2]

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

Ascores_set

BmemberX

CmemberY

Dscore_set

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the sorted set key and member name.

Using a wrong sorted set key.

The command ZSCORE scores_set memberX returns the score of memberX in the sorted set scores_set.

5fill in blank

hard

Fill all three blanks to get the score of 'playerA' from 'ranking_list' using the correct command format.

Redis

[1] [2] [3]

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

AZSCORE

Branking_list

CplayerA

DZADD

Attempts:

3 left

💡 Hint

Common Mistakes

Using ZADD instead of ZSCORE.

Swapping the order of arguments.

The correct command is ZSCORE ranking_list playerA to get the score of playerA from the sorted set ranking_list.

Practice

1. What does the Redis command ZSCORE do?

easy

A. Returns all members of a sorted set

B. Deletes a member from a sorted set

C. Returns the score of a member in a sorted set

D. Adds a member with a score to a sorted set

Solution

1. Step 1: Understand the purpose of ZSCORE

   The ZSCORE command is used to get the score associated with a specific member in a sorted set.

2. Step 2: Compare with other commands

   Other commands like ZADD add members, ZREM deletes members, and ZRANGE lists members, so they do not return scores directly.

3. Final Answer:

   Returns the score of a member in a sorted set -> Option C

4. Quick Check:

   ZSCORE = get member score [OK]

Hint: ZSCORE always fetches a member's score in sorted sets [OK]

Common Mistakes:

• Confusing ZSCORE with ZADD or ZREM
• Thinking ZSCORE returns members instead of scores
• Assuming ZSCORE modifies the sorted set

2. Which of the following is the correct syntax to get the score of member user42 from sorted set leaderboard in Redis?

easy

A. ZSCORE leaderboard user42

B. ZSCORE user42 leaderboard

C. ZGETSCORE leaderboard user42

D. ZGET leaderboard user42

Solution

1. Step 1: Recall the correct command format

   The correct syntax for ZSCORE is: ZSCORE key member. Here, leaderboard is the key and user42 is the member.

2. Step 2: Eliminate incorrect options

   Options B, C, and D either reverse the order or use invalid commands like ZGETSCORE or ZGET, which do not exist.

3. Final Answer:

   ZSCORE leaderboard user42 -> Option A

4. Quick Check:

   ZSCORE key member = ZSCORE leaderboard user42 [OK]

Hint: Remember: ZSCORE key member order is fixed [OK]

Common Mistakes:

• Swapping key and member positions
• Using non-existent commands like ZGET or ZGETSCORE
• Missing the key or member argument

3. Given the sorted set players with members and scores: {"alice": 50, "bob": 75, "carol": 60}, what will be the result of ZSCORE players bob?

medium

A. 75

B. 50

C. 60

D. nil

Solution

1. Step 1: Identify the member's score in the sorted set

   Member bob has a score of 75 in the players sorted set.

2. Step 2: Understand ZSCORE output

   The command ZSCORE players bob returns the score of bob, which is 75.

3. Final Answer:

   75 -> Option A

4. Quick Check:

   bob's score = 75 [OK]

Hint: ZSCORE returns the exact score of the member [OK]

Common Mistakes:

• Confusing scores of different members
• Expecting a list instead of a single score
• Assuming nil if member exists

4. You run the command ZSCORE leaderboard player1 but get (nil) as a result. What could be the reason?

medium

A. The member player1 has a score of 0

B. The member player1 is not in the sorted set

C. The command syntax is incorrect

D. Redis server is down

Solution

1. Step 1: Understand what (nil) means in ZSCORE

   When ZSCORE returns (nil), it means the member does not exist in the sorted set.

2. Step 2: Check other possibilities

   A score of 0 for player1 would return "0", not (nil). Syntax errors cause error messages, not (nil). Server down would cause connection errors.

3. Final Answer:

   The member player1 is not in the sorted set -> Option B

4. Quick Check:

   Member missing = (nil) result [OK]

Hint: (nil) means member not found in sorted set [OK]

Common Mistakes:

• Thinking (nil) means the score is 0
• Assuming (nil) means syntax error
• Thinking (nil) means server issue

5. You have a sorted set tasks with members and scores: {"task1": 10, "task2": 20, "task3": 30}. You want to check if task4 exists and get its score or return 0 if it doesn't. Which Redis command sequence achieves this?

hard

A. Use ZRANK tasks task4 to get score or 0

B. Use ZGET tasks task4 to get score or 0

C. Use ZCOUNT tasks task4 task4 to get score or 0

D. Use ZSCORE tasks task4 and if result is nil, treat score as 0

Solution

1. Step 1: Identify how to get a member's score safely

   ZSCORE returns the score or (nil) if the member does not exist.

2. Step 2: Handle missing member case

   Since ZSCORE returns (nil) for missing members, you can check this result and treat it as 0 in your application logic.

3. Step 3: Evaluate other options

   ZGET does not exist, ZRANK returns rank, not score, and ZCOUNT counts members in score range, not score value.

4. Final Answer:

   Use ZSCORE tasks task4 and if result is nil, treat score as 0 -> Option D

5. Quick Check:

   ZSCORE + nil check = safe score retrieval [OK]

Hint: Use ZSCORE and handle nil as zero in your code [OK]

Common Mistakes:

• Using non-existent commands like ZGET
• Confusing rank with score using ZRANK
• Using ZCOUNT which counts members, not scores