GETRANGE and SETRANGE in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of GETRANGE after SETRANGE?

Given a Redis key mykey with initial value "Hello World", what will be the result of GETRANGE mykey 6 10 after running SETRANGE mykey 6 "Redis"?

Redis

SET mykey "Hello World"
SETRANGE mykey 6 "Redis"
GETRANGE mykey 6 10

A "World"

B "Redis"

C "Redisorld"

D "Hello"

💡 Hint

Remember SETRANGE replaces part of the string starting at the given offset.

The SETRANGE command replaces the substring starting at index 6 with "Redis", so the string becomes "Hello Redis". Then GETRANGE from 6 to 10 returns "Redis".

❓ query_result

intermediate

What does GETRANGE return for out-of-bound indexes?

If the Redis key msg has value "OpenAI", what is the result of GETRANGE msg 3 10?

Redis

SET msg "OpenAI"
GETRANGE msg 3 10

A "nAI"

B "nAI\u0000\u0000\u0000\u0000"

C "OpenAI"

D ""

💡 Hint

GETRANGE returns substring up to the end if end index is beyond string length.

The string "OpenAI" has length 6. GETRANGE from index 3 to 10 returns substring from 3 to end, which is "nAI".

📝 Syntax

advanced

Which SETRANGE command is syntactically correct?

Choose the correct syntax to replace part of the string stored at key data starting at offset 4 with "Test".

A SETRANGE data "4" "Test"

B SETRANGE data 4 Test

C SETRANGE data 4 "Test"

D SETRANGE data 4 'Test'

💡 Hint

The offset must be an integer and the value a string enclosed in quotes.

SETRANGE requires the offset as an integer and the value as a string. Option C correctly uses integer 4 and string "Test".

❓ optimization

advanced

Efficiently update a substring in a large Redis string

You have a large string stored in Redis key bigtext. You want to replace characters from position 1000 to 1004 with "Hello". Which command is the most efficient?

A SETRANGE bigtext 1000 "Hello"

B

GET bigtext
Modify substring in client
SET bigtext modified_string

C APPEND bigtext "Hello"

D

GETRANGE bigtext 0 999
APPEND "Hello"

💡 Hint

SETRANGE modifies the string in place without transferring the whole string.

SETRANGE modifies the string directly on the server at the specified offset, avoiding large data transfer.

🧠 Conceptual

expert

What happens if SETRANGE offset is beyond current string length?

If the Redis key key1 has value "abc", what is the result of SETRANGE key1 5 "xyz" followed by GET key1?

Redis

SET key1 "abc"
SETRANGE key1 5 "xyz"
GET key1

A "abc xyz"

B Error: offset out of range

C "abcxyz"

D "abc\u0000\u0000xyz"

💡 Hint

SETRANGE pads with zero-bytes if offset is beyond string length.

SETRANGE pads the string with zero-bytes (\u0000) up to the offset before inserting the new substring.

Practice

1. What does the Redis command GETRANGE key 0 4 do?

easy

A. Returns the substring of the value stored at key from index 0 to 4 inclusive.

B. Deletes the first 5 characters of the string stored at key.

C. Replaces the first 5 characters of the string stored at key with zeros.

D. Returns the length of the string stored at key.

Solution

1. Step 1: Understand GETRANGE parameters

   The command GETRANGE key start end returns the substring from the start index to the end index inclusive.

2. Step 2: Apply to given indices

   With start=0 and end=4, it returns characters at positions 0,1,2,3,4 from the string stored at key.

3. Final Answer:

   Returns substring from index 0 to 4 inclusive -> Option A

4. Quick Check:

   GETRANGE extracts substring = A [OK]

Hint: GETRANGE extracts substring by start and end indexes [OK]

Common Mistakes:

• Thinking GETRANGE deletes or modifies the string
• Confusing GETRANGE with SETRANGE
• Assuming end index is exclusive

2. Which of the following is the correct syntax to replace part of a string value in Redis using SETRANGE?

easy

A. SETRANGE key value offset

B. SETRANGE key offset value

C. SET key offset value

D. GETRANGE key offset value

Solution

1. Step 1: Recall SETRANGE syntax

   The correct syntax is SETRANGE key offset value, where offset is the start position to replace and value is the new substring.

2. Step 2: Check options

   Only SETRANGE key offset value matches this syntax exactly.

3. Final Answer:

   SETRANGE key offset value -> Option B

4. Quick Check:

   Correct SETRANGE syntax = A [OK]

Hint: Remember SETRANGE order: key, offset, then value [OK]

Common Mistakes:

• Swapping offset and value positions
• Using GETRANGE instead of SETRANGE
• Using SET instead of SETRANGE

3. Given the Redis string value at key mykey is "HelloWorld", what will be the result of GETRANGE mykey 5 7?

medium

A. "World"

B. "Hello"

C. "loW"

D. "Wor"

Solution

1. Step 1: Identify substring indices

   The string is "HelloWorld" with indices: H(0), e(1), l(2), l(3), o(4), W(5), o(6), r(7), l(8), d(9).

2. Step 2: Extract substring from index 5 to 7

   Characters at 5,6,7 are 'W', 'o', 'r', so the substring is "Wor".

3. Final Answer:

   "Wor" -> Option D

4. Quick Check:

   GETRANGE returns substring = B [OK]

Hint: Count string indexes from 0 to get substring [OK]

Common Mistakes:

• Counting indexes starting at 1
• Including characters outside the range
• Confusing GETRANGE with SETRANGE

4. You run SETRANGE mykey 3 "abc" on a Redis string "abcdef". The result is unexpected. What is the likely mistake?

medium

A. Using quotes around the substring value in the command.

B. Offset 3 is out of range for the string length.

C. SETRANGE cannot modify existing strings.

D. The key mykey does not exist.

Solution

1. Step 1: Understand SETRANGE usage

   SETRANGE expects the substring value without quotes; quotes are interpreted literally.

2. Step 2: Identify the mistake

   Using quotes like "abc" inserts the quotes as characters, causing unexpected results.

3. Final Answer:

   Using quotes around substring causes wrong replacement -> Option A

4. Quick Check:

   Quotes in SETRANGE value cause errors = C [OK]

Hint: Do not include quotes around substring in SETRANGE [OK]

Common Mistakes:

• Including quotes around substring value
• Assuming offset must be within string length
• Thinking SETRANGE creates new keys automatically

5. If the Redis key text holds the string "abcdefghij", what will be the final string after executing SETRANGE text 5 "XYZ" followed by GETRANGE text 3 7?

hard

A. "defgh"

B. "fghij"

C. "deXYZ"

D. "defXY"

Solution

1. Step 1: Apply SETRANGE at offset 5

   Original string: "abcdefghij". SETRANGE replaces characters at positions 5,6,7 with "XYZ". Positions: a(0), b(1), c(2), d(3), e(4), f(5), g(6), h(7), i(8), j(9). After replacement: "abcdeXYZij".

2. Step 2: Apply GETRANGE from 3 to 7

   Characters at positions 3 to 7 are: d(3), e(4), X(5), Y(6), Z(7). So substring is "deXYZ".

3. Final Answer:

   "deXYZ" -> Option C

4. Quick Check:

   SETRANGE modifies substring, GETRANGE extracts it = D [OK]

Hint: Apply SETRANGE first, then GETRANGE on updated string [OK]

Common Mistakes:

• Not updating string before GETRANGE
• Miscounting offset positions
• Assuming GETRANGE returns original string