ZRANGEBYLEX for lexicographic queries in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Redis command ZRANGEBYLEX do?

ZRANGEBYLEX returns members in a sorted set within a specified lexicographic range.

It sorts by dictionary order, not by score.

beginner

How do you specify an inclusive range in ZRANGEBYLEX?

Use square brackets [ before the value.

Example: [apple means include 'apple' in the range.

beginner

What symbols indicate exclusive range boundaries in ZRANGEBYLEX?

Use parentheses ( before the value.

Example: (apple means exclude 'apple' from the range.

beginner

What do the special values - and + mean in ZRANGEBYLEX?

- means the smallest possible value (start of range).

+ means the largest possible value (end of range).

beginner

Can ZRANGEBYLEX be used to query by score in Redis sorted sets?

No. ZRANGEBYLEX queries by lexicographic order of members, ignoring scores.

Use ZRANGEBYSCORE to query by score.

What does ZRANGEBYLEX myset [a (c return?

A Members from 'a' exclusive up to 'c' inclusive

B Members from 'a' inclusive up to 'c' exclusive

C Members from 'a' exclusive up to 'c' exclusive

D Members from 'a' inclusive up to 'c' inclusive

Square bracket [ means inclusive, parenthesis ( means exclusive.

So range is from 'a' inclusive to 'c' exclusive.

Which command would you use to get all members lexicographically greater than 'mango'?

A ZRANGEBYLEX myset (mango +

B ZRANGEBYLEX myset [mango +

C ZRANGEBYSCORE myset (mango +

D ZRANGEBYLEX myset - (mango

(mango means exclude 'mango', + means max value.

This returns members greater than 'mango'.

What does the - symbol mean in ZRANGEBYLEX?

A Include the member

B Largest possible member

C Exclude the member

D Smallest possible member

- means the smallest possible member in lexicographic order.

If you want to include 'banana' in the range, which prefix do you use?

A [banana

B (banana

C -banana

D +banana

Square bracket [ means include the member.

Can ZRANGEBYLEX return members sorted by their scores?

A Yes, if you specify a score range

B Yes, it sorts by score

C No, it sorts by lexicographic order only

D No, it returns random members

ZRANGEBYLEX sorts members by their lexicographic order, ignoring scores.

Explain how to use ZRANGEBYLEX to get members between two lexicographic values, including how to specify inclusive and exclusive ranges.

Think about how dictionary order works and how to include or exclude boundary words.

Describe the difference between ZRANGEBYLEX and ZRANGEBYSCORE in Redis sorted sets.

One sorts by words, the other by numbers.

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