ZRANGEBYLEX for lexicographic queries in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this ZRANGEBYLEX query?

Given a sorted set myzset with members a, b, c, d, and e, what does the command ZRANGEBYLEX myzset [b [d return?

Redis

ZRANGEBYLEX myzset [b [d

A ["b", "c", "d"]

B ["c", "d"]

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

D ["b", "c"]

💡 Hint

Remember that square brackets mean inclusive range in lexicographic queries.

The command returns all members from 'b' to 'd' inclusive, so it includes 'b', 'c', and 'd'.

📝 Syntax

intermediate

Which ZRANGEBYLEX command is syntactically correct?

Choose the syntactically valid ZRANGEBYLEX command to get members lexicographically between 'a' (exclusive) and 'c' (inclusive).

A ZRANGEBYLEX myzset [a [c

B ZRANGEBYLEX myzset [a (c

C ZRANGEBYLEX myzset (a (c

D ZRANGEBYLEX myzset (a [c

💡 Hint

Parentheses mean exclusive, square brackets mean inclusive in ZRANGEBYLEX.

Option D correctly uses (a for exclusive start and [c for inclusive end, matching the requirement.

❓ optimization

advanced

How to optimize a ZRANGEBYLEX query for large sorted sets?

You want to retrieve members lexicographically between 'm' and 'z' from a very large sorted set. Which approach optimizes performance best?

A Use ZRANGEBYLEX with a small range and LIMIT option to paginate results.

B Use ZRANGEBYSCORE instead with scores converted from lexicographic values.

C Use ZRANGEBYLEX with exclusive ranges to reduce returned members.

D Use ZRANGEBYLEX without LIMIT to get all results at once.

💡 Hint

Fetching large ranges at once can be slow; pagination helps.

Using LIMIT with ZRANGEBYLEX paginates results, reducing memory and network load.

🔧 Debug

advanced

Why does this ZRANGEBYLEX command return an empty list?

Given a sorted set with members 'apple', 'banana', 'cherry', 'date', why does ZRANGEBYLEX myzset (banana (cherry return an empty list?

A Because the sorted set is empty.

B Because the command syntax is invalid and causes an error.

C Because the range excludes both 'banana' and 'cherry', and no members lie strictly between them.

D Because the range should use square brackets instead of parentheses.

💡 Hint

Parentheses exclude the boundary members.

The range excludes 'banana' and 'cherry' and no other members are lexicographically between them.

🧠 Conceptual

expert

What is the difference between ZRANGEBYLEX and ZRANGEBYSCORE?

Which statement best describes the difference between ZRANGEBYLEX and ZRANGEBYSCORE commands in Redis sorted sets?

A ZRANGEBYLEX queries by numeric score values, ZRANGEBYSCORE queries by lexicographic order.

B ZRANGEBYLEX queries members by their lexicographic order ignoring scores, while ZRANGEBYSCORE queries by numeric score values.

C Both commands query by score but ZRANGEBYLEX is faster.

D ZRANGEBYLEX only works on sets with string scores, ZRANGEBYSCORE only on numeric members.

💡 Hint

Think about what 'lex' and 'score' mean.

ZRANGEBYLEX uses the member strings' lexicographic order ignoring scores; ZRANGEBYSCORE uses numeric scores.

Practice

1. What does the Redis command ZRANGEBYLEX do?

easy

A. Returns members sorted by their score in descending order.

B. Returns members in a sorted set within a lexicographic range.

C. Deletes members from a sorted set based on lexicographic order.

D. Adds members to a sorted set with a lexicographic score.

Solution

1. Step 1: Understand the command purpose

   ZRANGEBYLEX is used to get members from a sorted set based on their alphabetical order, not their score.

2. Step 2: Compare options with command behavior

   Only Returns members in a sorted set within a lexicographic range. correctly describes that it returns members within a lexicographic range. Other options confuse sorting by score or modifying the set.

3. Final Answer:

   Returns members in a sorted set within a lexicographic range. -> Option B

4. Quick Check:

   ZRANGEBYLEX = Lexicographic range retrieval [OK]

Hint: ZRANGEBYLEX fetches by alphabetical order, not score [OK]

Common Mistakes:

• Confusing lexicographic order with score order
• Thinking it deletes or adds members
• Assuming it sorts in descending order

2. Which of the following is the correct syntax to get members from 'myzset' between 'a' and 'c' inclusive using ZRANGEBYLEX?

easy

A. ZRANGEBYLEX myzset [a [c

B. ZRANGEBYLEX myzset (a (c

C. ZRANGEBYLEX myzset a c

D. ZRANGEBYLEX myzset {a {c

Solution

1. Step 1: Recall syntax for inclusive range

   In ZRANGEBYLEX, square brackets [ ] mean inclusive boundaries.

2. Step 2: Match syntax with options

   ZRANGEBYLEX myzset [a [c uses [a and [c, correctly including both 'a' and 'c'. Other options use parentheses or braces which mean exclusive or invalid.

3. Final Answer:

   ZRANGEBYLEX myzset [a [c -> Option A

4. Quick Check:

   Inclusive range uses [ ] brackets [OK]

Hint: Use [ ] for inclusive, ( ) for exclusive in ZRANGEBYLEX [OK]

Common Mistakes:

• Using parentheses instead of brackets for inclusive range
• Omitting brackets causing syntax errors
• Using curly braces which are invalid here

3. Given a sorted set 'myzset' with members: ['apple', 'banana', 'carrot', 'date', 'egg'], what is the result of ZRANGEBYLEX myzset [banana (date?

medium

A. ['banana', 'carrot', 'date', 'egg']

B. ['banana', 'carrot', 'date']

C. ['carrot', 'date']

D. ['banana', 'carrot']

Solution

1. Step 1: Understand the range boundaries

   Start is inclusive [banana], end is exclusive (date), so 'date' is not included.

2. Step 2: Select members in range

   Members between 'banana' and before 'date' are 'banana' and 'carrot'. 'date' and 'egg' are excluded.

3. Final Answer:

   ['banana', 'carrot'] -> Option D

4. Quick Check:

   Inclusive start, exclusive end excludes 'date' [OK]

Hint: Remember ( ) excludes the boundary member [OK]

Common Mistakes:

• Including 'date' despite exclusive end
• Including 'egg' which is outside range
• Confusing inclusive and exclusive boundaries

4. You run ZRANGEBYLEX myzset [a [z LIMIT 0 2 but get an error. What is the likely cause?

medium

A. LIMIT requires both offset and count as integers.

B. LIMIT must come before the range arguments.

C. Range boundaries must use parentheses, not brackets.

D. myzset does not exist, causing the error.

Solution

1. Step 1: Check LIMIT syntax

   LIMIT requires two integer arguments: offset and count. If either is missing or not integer, error occurs.

2. Step 2: Compare options

   LIMIT requires offset and count to be valid integers; non-integer values (e.g., strings like "two" or malformed) cause syntax errors. Other options are incorrect: LIMIT follows the range arguments (not B), brackets are valid for inclusive (not C), non-existent key returns empty list (not D).

3. Final Answer:

   LIMIT requires both offset and count as integers. -> Option A

4. Quick Check:

   LIMIT needs two integer args [OK]

Hint: LIMIT needs two integers: offset and count [OK]

Common Mistakes:

• Using LIMIT with missing or non-integer arguments
• Placing LIMIT before range arguments
• Confusing bracket types for range boundaries

5. You want to get exactly 3 members from 'myzset' starting after 'apple' (exclusive) up to 'date' (inclusive). Which command is correct?

hard

A. ZRANGEBYLEX myzset (apple (date LIMIT 0 3

B. ZRANGEBYLEX myzset [apple [date LIMIT 1 3

C. ZRANGEBYLEX myzset (apple [date LIMIT 0 3

D. ZRANGEBYLEX myzset [apple (date LIMIT 0 3

Solution

1. Step 1: Set correct range boundaries

   Start after 'apple' means exclusive start: (apple). End up to 'date' inclusive means [date].

2. Step 2: Use LIMIT to get 3 members from start

   LIMIT 0 3 means start at offset 0 and get 3 members.

3. Step 3: Verify options

   Only ZRANGEBYLEX myzset (apple [date LIMIT 0 3 matches exclusive start, inclusive end, and correct LIMIT usage.

4. Final Answer:

   ZRANGEBYLEX myzset (apple [date LIMIT 0 3 -> Option C

5. Quick Check:

   Exclusive start ( ), inclusive end [ ], LIMIT 0 3 [OK]

Hint: Use ( for exclusive start, [ for inclusive end, LIMIT 0 3 for 3 items [OK]

Common Mistakes:

• Using inclusive start when exclusive is needed
• Mixing up LIMIT offset and count
• Using wrong bracket types for boundaries