SET and GET commands in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this Redis command sequence?

Consider the following Redis commands executed in order:

SET user:1 "Alice"
GET user:1

What will the GET command return?

Redis

SET user:1 "Alice"
GET user:1

A "Alice"

B user:1

C nil

D Error: key not found

💡 Hint

The SET command stores a value for a key. GET retrieves that value.

The SET command stores the string "Alice" under the key "user:1". The GET command then returns the stored value, which is "Alice".

❓ query_result

intermediate

What happens when you GET a non-existing key?

If you run the command GET missing_key on Redis where no such key exists, what is the output?

Redis

GET missing_key

A (nil)

B "missing_key"

C Error: key not found

D ""

💡 Hint

Redis returns a special value when keys are missing.

When a key does not exist, Redis returns nil to indicate no value is stored.

📝 Syntax

advanced

Which command syntax correctly sets a key with expiration of 10 seconds?

You want to set key "session" with value "xyz" that expires after 10 seconds. Which command is correct?

A SET session xyz PX 10

B SET session xyz TTL 10

C SET session xyz EXPIRE 10

D SET session xyz EX 10

💡 Hint

EX sets expiration in seconds, PX in milliseconds.

The correct syntax to set expiration in seconds is using EX option with SET command.

❓ query_result

advanced

What is the output after overwriting a key?

Given these commands:

SET color "red"
SET color "blue"
GET color

What does the GET command return?

Redis

SET color "red"
SET color "blue"
GET color

A nil

B "red"

C "blue"

D Error: key already exists

💡 Hint

SET overwrites existing keys with new values.

The second SET command overwrites the value of "color" to "blue". GET returns the latest value.

🧠 Conceptual

expert

Why does GET return nil after key expiration?

You set a key with expiration using SET key value EX 5. After 6 seconds, you run GET key. Why does it return nil?

A GET command cannot retrieve keys with expiration set.

B The key automatically deletes after expiration time, so GET finds no key.

C Redis caches old values and returns nil if cache expires.

D The key value is hidden but still exists, GET returns nil by design.

💡 Hint

Expiration removes the key from the database.

When a key expires, Redis deletes it automatically. GET then returns nil because the key no longer exists.