Range queries for scoring in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Retrieve members with scores between 50 and 100

Given a sorted set players with player names as members and their scores as scores, which Redis command returns all players with scores between 50 and 100 inclusive?

Redis

ZADD players 30 "Alice" 60 "Bob" 90 "Charlie" 110 "Diana"

A ZRANGEBYSCORE players 50 100

B ZRANGE players 50 100

C ZREVRANGEBYSCORE players 50 100

D ZRANGEBYSCORE players (50 (100

💡 Hint

Use the command that filters by score range, not by rank.

ZRANGEBYSCORE returns members with scores within the specified range. ZRANGE uses rank indexes, not scores. ZREVRANGEBYSCORE reverses the order but requires the max score first. Parentheses indicate exclusive bounds, so option A excludes 50 and 100.

📝 Syntax

intermediate

Identify the syntax error in this Redis range query

Which option contains a syntax error when trying to get members with scores between 20 and 80 from sorted set scores?

Redis

ZADD scores 10 "x" 30 "y" 70 "z"

A ZRANGEBYSCORE scores 20 80

B ZRANGEBYSCORE scores 20, 80

C ZRANGEBYSCORE scores (20 80

D ZRANGEBYSCORE scores 20 (80

💡 Hint

Check for invalid characters or separators in the command.

Option B uses a comma between scores, which is invalid syntax. Scores must be separated by space only. Options B, C, and D are valid syntax with inclusive or exclusive bounds.

❓ optimization

advanced

Efficiently retrieve top 5 players with scores above 90

You want to get the top 5 players with scores greater than 90 from sorted set leaderboard. Which command is the most efficient and correct?

Redis

ZADD leaderboard 85 "Anna" 92 "Ben" 95 "Cara" 99 "Dave" 100 "Eve" 88 "Fay"

A ZRANGEBYSCORE leaderboard (90 +inf LIMIT 0 5

B ZRANGEBYSCORE leaderboard 90 +inf LIMIT 0 5

C ZREVRANGEBYSCORE leaderboard +inf (90 LIMIT 0 5

D ZREVRANGEBYSCORE leaderboard +inf 90 LIMIT 0 5

💡 Hint

Remember that ZREVRANGEBYSCORE returns members in descending score order.

Option C correctly uses ZREVRANGEBYSCORE with exclusive lower bound (90) and upper bound +inf, limiting to 5 results. Option C uses ZRANGEBYSCORE which returns ascending order, not top scores. Option C includes 90 (not strictly greater). Option C uses inclusive 90, including players with score 90.

🔧 Debug

advanced

Why does this range query return no results?

You run the command ZRANGEBYSCORE games 100 50 on a sorted set games with scores from 10 to 150, but get an empty list. Why?

Redis

ZADD games 10 "g1" 50 "g2" 100 "g3" 150 "g4"

A ZRANGEBYSCORE only works with integer scores

B ZRANGEBYSCORE requires the max score first, then min score

C The sorted set is empty, so no results

D The min score is greater than max score; range is invalid

💡 Hint

Check the order of min and max scores in the command.

ZRANGEBYSCORE expects min score first, then max score. Here min=100 and max=50 is invalid, so no members match. Option D is incorrect because min must come first. The set is not empty, and scores can be floats.

🧠 Conceptual

expert

Understanding exclusive and inclusive bounds in Redis range queries

Which option correctly describes the difference between ZRANGEBYSCORE key (50 100 and ZRANGEBYSCORE key 50 (100?

A The first excludes 50 but includes 100; the second includes 50 but excludes 100

B Both exclude 50 and 100

C The first includes 50 and excludes 100; the second excludes 50 and includes 100

D Both include 50 and 100

💡 Hint

Parentheses before a score mean exclusive bound for that score.

In Redis, a parenthesis before a score means exclusive. So (50 excludes 50, 50 includes it. The first command excludes 50 but includes 100. The second includes 50 but excludes 100.

Practice

1. What does the Redis command ZRANGEBYSCORE do?

easy

A. It returns members in a sorted set within a specified score range.

B. It deletes members from a sorted set based on score.

C. It adds new members to a sorted set with scores.

D. It returns the total number of members in a sorted set.

Solution

1. Step 1: Understand the command purpose

   ZRANGEBYSCORE is used to get members from a sorted set filtered by score range.

2. Step 2: Compare options with command behavior

   Only "It returns members in a sorted set within a specified score range." correctly describes returning members within a score range.

3. Final Answer:

   It returns members in a sorted set within a specified score range. -> Option A

4. Quick Check:

   ZRANGEBYSCORE = returns members by score range [OK]

Hint: ZRANGEBYSCORE fetches members filtered by score range [OK]

Common Mistakes:

• Confusing ZRANGEBYSCORE with commands that add or delete members
• Thinking it returns count instead of members
• Assuming it sorts members by name instead of score

2. Which of the following is the correct syntax to get members with scores between 10 and 20 from a sorted set named myzset?

easy

A. ZRANGEBYSCORE myzset [10 [20

B. ZRANGEBYSCORE myzset (10 (20

C. ZRANGEBYSCORE myzset 10 20

D. ZRANGEBYSCORE myzset "10" "20"

Solution

1. Step 1: Recall basic syntax of ZRANGEBYSCORE

   The command format is ZRANGEBYSCORE key min max where min and max are numbers or special strings.

2. Step 2: Analyze options for correct syntax

   ZRANGEBYSCORE myzset 10 20 uses plain numbers 10 and 20 correctly. Options A and B use parentheses or brackets which mean exclusive or inclusive but are not needed here. ZRANGEBYSCORE myzset "10" "20" uses quotes which are unnecessary.

3. Final Answer:

   ZRANGEBYSCORE myzset 10 20 -> Option C

4. Quick Check:

   Syntax = ZRANGEBYSCORE key min max [OK]

Hint: Use plain numbers for inclusive score range in ZRANGEBYSCORE [OK]

Common Mistakes:

• Using parentheses or brackets incorrectly for inclusive ranges
• Adding quotes around numeric scores
• Mixing up min and max order

3. Given the sorted set myzset with members and scores: {"a":5, "b":10, "c":15, "d":20}, what is the result of ZRANGEBYSCORE myzset 10 20 WITHSCORES?

medium

A. ["b", "10", "c", "15", "d", "20"]

B. ["a", "5", "b", "10", "c", "15"]

C. ["c", "15", "d", "20"]

D. ["a", "5", "d", "20"]

Solution

1. Step 1: Identify members with scores between 10 and 20 inclusive

   Members with scores 10, 15, and 20 are "b", "c", and "d" respectively.

2. Step 2: Understand WITHSCORES option output

   WITHSCORES returns members and their scores as alternating elements in the list.

3. Final Answer:

   ["b", "10", "c", "15", "d", "20"] -> Option A

4. Quick Check:

   Members with scores 10-20 + WITHSCORES = ["b", "10", "c", "15", "d", "20"] [OK]

Hint: WITHSCORES returns member-score pairs in order [OK]

Common Mistakes:

• Including members outside the score range
• Returning only members without scores
• Mixing order of members and scores

4. What is wrong with this command to get members with scores between 5 and 15 from myzset?

ZRANGEBYSCORE myzset 5 15 WITHSCORE

medium

A. The score range should be reversed as 15 5.

B. The option should be WITHSCORES, not WITHSCORE.

C. The command needs a LIMIT clause to work.

D. The key name must be quoted.

Solution

1. Step 1: Check the option spelling

   The correct option to include scores is WITHSCORES (plural), not WITHSCORE.

2. Step 2: Verify other parts of the command

   The score range 5 to 15 is correct, LIMIT is optional, and key names do not require quotes.

3. Final Answer:

   The option should be WITHSCORES, not WITHSCORE. -> Option B

4. Quick Check:

   Correct option spelling = WITHSCORES [OK]

Hint: Use WITHSCORES (plural) to get scores with members [OK]

Common Mistakes:

• Misspelling WITHSCORES option
• Reversing min and max scores
• Adding unnecessary quotes around key

5. You have a sorted set players with player names and their scores. You want to find all players with scores greater than 50 but less than or equal to 100, including their scores. Which command correctly achieves this?

hard

A. ZRANGEBYSCORE players [50 100 WITHSCORES

B. ZRANGEBYSCORE players 50 100 WITHSCORES

C. ZRANGEBYSCORE players (50 (100 WITHSCORES

D. ZRANGEBYSCORE players (50 100 WITHSCORES

Solution

1. Step 1: Understand score range requirements

   Scores must be greater than 50 (exclusive) and less than or equal to 100 (inclusive).

2. Step 2: Use parentheses for exclusive and plain number for inclusive

   In Redis, (50 means greater than 50 (exclusive), and 100 means less than or equal to 100 (inclusive).

3. Step 3: Check command syntax

   ZRANGEBYSCORE players (50 100 WITHSCORES correctly uses (50 and 100 with WITHSCORES option.

4. Final Answer:

   ZRANGEBYSCORE players (50 100 WITHSCORES -> Option D

5. Quick Check:

   Exclusive lower bound uses (number) syntax [OK]

Hint: Use (number for exclusive, number for inclusive in range [OK]

Common Mistakes:

• Using brackets [] which Redis does not support for range
• Not using parentheses for exclusive bounds
• Confusing inclusive and exclusive range syntax