ZRANGEBYLEX for lexicographic queries in Redis

Introduction

ZRANGEBYLEX helps you get items from a sorted list based on alphabetical order, not numbers.

You want to find all names starting with a certain letter in a list.

You need to get all words between 'apple' and 'banana' alphabetically.

You want to list all items that come after 'cat' but before 'dog' in a dictionary.

You want to filter usernames that start with letters between 'a' and 'm'.

Syntax

Redis

ZRANGEBYLEX key min max [LIMIT offset count]

min and max define the lexicographic range using special characters: '[' means inclusive, '(' means exclusive, '-' means minimum, '+' means maximum.

LIMIT is optional and helps you get a smaller part of the results by skipping some and limiting how many you get.

Examples

Gets all items from 'myset' starting at 'apple' and including 'banana'.

Redis

ZRANGEBYLEX myset [apple [banana

Gets all items from 'myset' after 'apple' but before 'banana', excluding both.

Redis

ZRANGEBYLEX myset (apple (banana

Gets all items from 'myset' in alphabetical order.

Redis

ZRANGEBYLEX myset - +

Gets the first 3 items from 'myset' between 'cat' and 'dog', including both.

Redis

ZRANGEBYLEX myset [cat [dog LIMIT 0 3

Sample Program

We add fruits with score 0 (score is ignored for lex queries). Then we get fruits from 'banana' to 'fig' inclusive, sorted alphabetically.

Redis

127.0.0.1:6379> ZADD fruits 0 apple 0 banana 0 cherry 0 date 0 fig 0 grape
(integer) 6
127.0.0.1:6379> ZRANGEBYLEX fruits [banana [fig
1) "banana"
2) "cherry"
3) "date"
4) "fig"

Important Notes

ZRANGEBYLEX only works on sorted sets where all scores are the same or ignored; it sorts by member name alphabetically.

Time complexity is O(log(N)+M) where N is total elements and M is returned elements.

Common mistake: Using ZRANGEBYLEX on sorted sets with different scores expecting numeric order; it sorts by member name, not score.

Use ZRANGEBYLEX when you want alphabetical range queries; use ZRANGE for numeric score ranges.

Summary

ZRANGEBYLEX gets items from a sorted set based on alphabetical order.

Use '[' for inclusive and '(' for exclusive range boundaries.

LIMIT helps control how many results you get and where to start.

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