RENAME and RENAMENX in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the result of RENAME when the new key exists?

Assume the Redis database has keys: key1 with value 100 and key2 with value 200. What happens after running RENAME key1 key2?

Redis

SET key1 100
SET key2 200
RENAME key1 key2
GET key2

A Returns an error because key2 already exists

B Deletes both keys and returns nil

C Does nothing and returns OK; GET key2 returns 200

D Renames key1 to key2, overwriting the old key2 value; GET key2 returns 100

💡 Hint

RENAME overwrites the destination key if it exists.

The RENAME command changes the key name even if the new key exists, overwriting its value.

❓ query_result

intermediate

What does RENAMENX return if the new key exists?

Given keys alpha with value foo and beta with value bar, what is the return value of RENAMENX alpha beta?

Redis

SET alpha foo
SET beta bar
RENAMENX alpha beta

A 0, because beta already exists and rename did not happen

B 1, because the rename succeeded

C An error because beta exists

D nil, because alpha does not exist

💡 Hint

RENAMENX only renames if the new key does not exist.

RENAMENX returns 0 and does not rename if the new key exists.

📝 Syntax

advanced

Which command syntax is correct to rename a key only if the new key does not exist?

Choose the correct Redis command syntax to rename oldkey to newkey only if newkey does not exist.

A RENAMENX oldkey newkey

B RENAME oldkey newkey NX

C RENAME IF NOT EXISTS oldkey newkey

D RENAMEX oldkey newkey

💡 Hint

The command is RENAMENX, not RENAME with options.

RENAMENX is the correct command to rename only if the new key does not exist.

🧠 Conceptual

advanced

What happens if you RENAME a key to the same key name?

If you run RENAME mykey mykey in Redis, what is the result?

A Returns an error because source and destination are the same

B Deletes the key

C Returns OK and does nothing

D Renames the key to a new random key

💡 Hint

RENAME returns OK even if source and destination are the same.

The RENAME command returns OK even when the source and destination keys are the same, and the key remains unchanged.

🔧 Debug

expert

Why does RENAMENX fail to rename when the new key does not exist?

You run these commands: SET a 1 DEL b RENAMENX a b But RENAMENX returns 0 and does not rename. What is the most likely cause?

Redis

SET a 1
DEL b
RENAMENX a b

A Key 'b' still exists, so RENAMENX refuses to rename

B Key 'a' does not exist at the time of RENAMENX

C RENAMENX cannot rename keys with numeric values

D RENAMENX requires both keys to exist

💡 Hint

Check if the source key exists before renaming.

RENAMENX returns 0 if the source key does not exist, even if the destination key is missing.

Practice

1. What does the Redis command RENAME do?

easy

A. Changes the name of a key and overwrites the new key if it exists

B. Changes the name of a key only if the new key does not exist

C. Deletes a key without renaming

D. Creates a copy of a key with a new name

Solution

1. Step 1: Understand the purpose of RENAME

   The RENAME command changes the name of an existing key to a new name.

2. Step 2: Check behavior when new key exists

   If the new key already exists, RENAME overwrites it without error.

3. Final Answer:

   Changes the name of a key and overwrites the new key if it exists -> Option A

4. Quick Check:

   RENAME overwrites existing keys = B [OK]

Hint: RENAME always renames and overwrites existing keys [OK]

Common Mistakes:

• Thinking RENAME only renames if new key is free
• Confusing RENAME with RENAMENX
• Assuming RENAME copies instead of renaming

2. Which of the following is the correct syntax to rename a key oldkey to newkey using RENAMENX?

easy

A. RENAMENX newkey oldkey

B. RENAME oldkey newkey

C. RENAMENX oldkey newkey

D. RENAMEX oldkey newkey

Solution

1. Step 1: Recall RENAMENX syntax

   The correct syntax is RENAMENX oldkey newkey, where the first argument is the current key and the second is the new key.

2. Step 2: Identify incorrect options

   A reverses arguments, B uses RENAME not RENAMENX, D has a typo in command name.

3. Final Answer:

   RENAMENX oldkey newkey -> Option C

4. Quick Check:

   RENAMENX oldkey newkey syntax = C [OK]

Hint: Remember: RENAMENX oldkey newkey [OK]

Common Mistakes:

• Swapping oldkey and newkey arguments
• Using RENAME instead of RENAMENX
• Typo in command name

3. Given the following Redis commands executed in order:

SET key1 "value1"
SET key2 "value2"
RENAMENX key1 key2
GET key1
GET key2

What will be the output of the two GET commands?

medium

A. GET key1: "value1", GET key2: "value2"

B. GET key1: nil, GET key2: "value1"

C. GET key1: "value1", GET key2: "value1"

D. GET key1: nil, GET key2: "value2"

Solution

1. Step 1: Analyze RENAMENX behavior

   RENAMENX renames key1 to key2 only if key2 does not exist. Here, key2 exists, so RENAMENX does nothing.

2. Step 2: Check GET results

   Since RENAMENX failed, key1 still holds "value1" and key2 holds "value2".

3. Final Answer:

   GET key1: "value1", GET key2: "value2" -> Option A

4. Quick Check:

   RENAMENX fails if new key exists = A [OK]

Hint: RENAMENX fails if new key exists, keys unchanged [OK]

Common Mistakes:

• Assuming RENAMENX overwrites existing keys
• Expecting key1 to be deleted after RENAMENX
• Confusing RENAMENX with RENAME

4. You run the command RENAMENX keyA keyB but get an error saying ERR no such key. What is the most likely cause?

medium

A. keyB does not exist

B. RENAMENX command is misspelled

C. keyB already exists

D. keyA does not exist

Solution

1. Step 1: Understand error meaning

   The error ERR no such key means the source key to rename does not exist.

2. Step 2: Identify which key is source

   In RENAMENX keyA keyB, keyA is the source key. If it does not exist, the error occurs.

3. Final Answer:

   keyA does not exist -> Option D

4. Quick Check:

   ERR no such key means source key missing = D [OK]

Hint: ERR no such key means source key missing [OK]

Common Mistakes:

• Thinking error means destination key missing
• Assuming RENAMENX overwrites keys
• Ignoring command spelling

5. You want to rename a key session123 to user_session only if user_session does not exist, and get a confirmation if rename succeeded. Which Redis command and response should you use?

hard

A. Use RENAME session123 user_session and expect OK response

B. Use RENAMENX session123 user_session and expect 1 if renamed, 0 if not

C. Use RENAMENX user_session session123 and expect 1 if renamed

D. Use RENAME user_session session123 and expect OK response

Solution

1. Step 1: Choose command that renames only if new key is free

   RENAMENX renames only if the new key does not exist, perfect for this case.

2. Step 2: Understand RENAMENX response

   RENAMENX returns 1 if rename succeeded, 0 if new key exists and rename skipped.

3. Final Answer:

   Use RENAMENX session123 user_session and expect 1 if renamed, 0 if not -> Option B

4. Quick Check:

   RENAMENX returns 1 or 0 for success/failure = A [OK]

Hint: RENAMENX returns 1 if renamed, 0 if new key exists [OK]

Common Mistakes:

• Using RENAME which always overwrites
• Swapping source and destination keys
• Expecting OK response from RENAMENX