ZRANGEBYSCORE for score-based queries in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Output of ZRANGEBYSCORE with inclusive range

Given a sorted set 'players' with scores: {"Alice": 50, "Bob": 70, "Charlie": 70, "Diana": 90}, what is the output of the command ZRANGEBYSCORE players 50 70?

A ["Alice", "Bob", "Charlie"]

B ["Alice", "Diana"]

C ["Bob", "Charlie"]

D ["Alice", "Bob"]

💡 Hint

ZRANGEBYSCORE includes elements with scores equal to the min and max by default.

ZRANGEBYSCORE returns all elements with scores between the min and max inclusive. Here, Alice (50), Bob (70), and Charlie (70) are included.

❓ query_result

intermediate

ZRANGEBYSCORE with exclusive min and max

What is the result of ZRANGEBYSCORE players (50 (90 on the same sorted set as before?

A ["Bob", "Charlie"]

B ["Alice", "Bob", "Charlie"]

C ["Diana"]

D []

💡 Hint

Parentheses before a score mean exclusive range boundary.

The command excludes scores equal to 50 and 90, so only Bob and Charlie with score 70 are returned.

📝 Syntax

advanced

Identify the syntax error in ZRANGEBYSCORE usage

Which option contains a syntax error when trying to get elements with scores between 10 and 20?

A ZRANGEBYSCORE myset 10 (20

B ZRANGEBYSCORE myset (10 20

C ZRANGEBYSCORE myset 10 20 (LIMIT 0 5)

D ZRANGEBYSCORE myset 10 20

💡 Hint

Check the syntax for LIMIT usage in ZRANGEBYSCORE.

The LIMIT option requires the keyword LIMIT before offset and count, not parentheses around it.

❓ optimization

advanced

Optimizing ZRANGEBYSCORE for large sorted sets

You want to retrieve only the first 3 elements with scores between 100 and 200 from a large sorted set. Which command is the most efficient?

A ZRANGEBYSCORE myset (100 (200 LIMIT 0 3

B ZRANGEBYSCORE myset 100 200 LIMIT 0 3

C ZRANGEBYSCORE myset 100 200

D ZRANGEBYSCORE myset 100 200 LIMIT 3 0

💡 Hint

LIMIT offset count syntax helps reduce data transferred.

Using LIMIT 0 3 returns only the first 3 matching elements, reducing memory and network usage.

🧠 Conceptual

expert

Understanding ZRANGEBYSCORE with negative and positive infinity

What is the output of ZRANGEBYSCORE myset -inf +inf on a sorted set with elements {"a": 1, "b": 2, "c": 3}?

A ["a"]

B []

C ["c", "b", "a"]

D ["a", "b", "c"]

💡 Hint

Negative and positive infinity include all scores.

Using -inf and +inf as min and max returns all elements in ascending score order.

Practice

1. What does the Redis command ZRANGEBYSCORE do?

easy

A. It returns the rank of a member in a sorted set.

B. It deletes members from a sorted set by score.

C. It adds a member with a score to a sorted set.

D. It returns members in a sorted set within a given score range.

Solution

1. Step 1: Understand the command purpose

   ZRANGEBYSCORE is used to get members from a sorted set based on their scores.

2. Step 2: Compare options with command behavior

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

3. Final Answer:

   It returns members in a sorted set within a given score range. -> Option D

4. Quick Check:

   ZRANGEBYSCORE = returns members by score range [OK]

Hint: ZRANGEBYSCORE fetches by score range, not by rank or deletion [OK]

Common Mistakes:

• Confusing ZRANGEBYSCORE with ZREM (deletion)
• Thinking it returns rank instead of members
• Mixing it up with ZADD (adding members)

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

easy

A. ZRANGEBYSCORE myzset 10 20 INCLSCORES

B. ZRANGEBYSCORE myzset 10 20 WITHSCORE

C. ZRANGEBYSCORE myzset 10 20 WITHSCORES

D. ZRANGEBYSCORE myzset 10 20 SCORES

Solution

1. Step 1: Recall correct option for including scores

   The correct keyword to include scores in output is WITHSCORES.

2. Step 2: Check syntax correctness

   ZRANGEBYSCORE myzset 10 20 WITHSCORES uses the exact correct syntax: ZRANGEBYSCORE myzset 10 20 WITHSCORES.

3. Final Answer:

   ZRANGEBYSCORE myzset 10 20 WITHSCORES -> Option C

4. Quick Check:

   WITHSCORES keyword includes scores [OK]

Hint: Use WITHSCORES exactly to get scores with members [OK]

Common Mistakes:

• Misspelling WITHSCORES
• Using WITHSCORE or SCORES instead
• Omitting WITHSCORES when scores are needed

3. Given the sorted set myzset with members and scores:
"a"=5, "b"=10, "c"=15, "d"=20, "e"=25
What is the result of ZRANGEBYSCORE myzset 10 20 LIMIT 1 2?

medium

A. ["c", "d"]

B. ["b", "c", "d"]

C. ["b", "c"]

D. ["a", "b"]

Solution

1. Step 1: Identify members in score range 10 to 20

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

2. Step 2: Apply LIMIT 1 2

   LIMIT 1 2 means skip 1 member, then return next 2 members. Skipping "b", next two are "c", "d".

3. Final Answer:

   ["c", "d"] -> Option A

4. Quick Check:

   LIMIT skips then returns count [OK]

Hint: LIMIT offset count skips offset, returns count members [OK]

Common Mistakes:

• Ignoring LIMIT offset and returning from start
• Confusing score range with member count
• Including members outside score range

4. You run the command ZRANGEBYSCORE myzset (10 20 but get an error. What is the likely cause?

medium

A. Syntax error due to missing closing parenthesis after 20.

B. Incorrect use of parentheses for exclusive range; missing closing parenthesis.

C. Command is missing the key name.

D. Missing closing parenthesis for exclusive range syntax.

Solution

1. Step 1: Analyze the command syntax

   The command uses (10 to indicate exclusive minimum score 10, which is correct syntax.

2. Step 2: Identify the error

   The command ends with 20 without closing parenthesis or space, causing syntax error.

3. Final Answer:

   Syntax error due to missing closing parenthesis after 20. -> Option A

4. Quick Check:

   Exclusive range needs parentheses on score values [OK]

Hint: Check parentheses carefully for exclusive score ranges [OK]

Common Mistakes:

• Forgetting parentheses for exclusive ranges
• Missing spaces between arguments
• Using parentheses incorrectly around scores

5. You want to get the top 3 members with scores between 0 and 100 from sorted set myzset, including their scores, but only if their score is greater than 50. Which command achieves this?

hard

A. ZRANGEBYSCORE myzset 50 100 WITHSCORES LIMIT 0 3

B. ZRANGEBYSCORE myzset (50 100 WITHSCORES LIMIT 0 3

C. ZRANGEBYSCORE myzset [50 100 WITHSCORES LIMIT 0 3

D. ZRANGEBYSCORE myzset (50 100 LIMIT 3 WITHSCORES

Solution

1. Step 1: Define score range with exclusive lower bound

   To get scores greater than 50, use (50 for exclusive minimum.

2. Step 2: Include scores and limit results

   Use WITHSCORES to include scores and LIMIT 0 3 to get top 3 members.

3. Step 3: Verify command syntax

   ZRANGEBYSCORE myzset (50 100 WITHSCORES LIMIT 0 3 correctly uses ZRANGEBYSCORE myzset (50 100 WITHSCORES LIMIT 0 3.

4. Final Answer:

   ZRANGEBYSCORE myzset (50 100 WITHSCORES LIMIT 0 3 -> Option B

5. Quick Check:

   Exclusive range + WITHSCORES + LIMIT = correct command [OK]

Hint: Use (score for exclusive, WITHSCORES, then LIMIT offset count [OK]

Common Mistakes:

• Using inclusive 50 instead of exclusive
• Placing LIMIT before WITHSCORES
• Using wrong bracket types for exclusive range