HMSET and HMGET for bulk in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this HMGET command?

Given the following Redis commands:

HMSET user:1 name "Alice" age "30" city "Paris"
HMGET user:1 name city

What is the output of the HMGET command?

Redis

HMSET user:1 name "Alice" age "30" city "Paris"
HMGET user:1 name city

A ["Alice", null]

B ["Alice", "Paris"]

C ["name", "city"]

D ["30", "Paris"]

💡 Hint

HMGET returns the values of the specified fields in the order requested.

HMSET sets multiple fields in a hash. HMGET retrieves the values of the specified fields. Here, 'name' and 'city' fields are requested, so their values 'Alice' and 'Paris' are returned in a list.

📝 Syntax

intermediate

Which HMSET command is syntactically correct?

Choose the correct syntax for setting multiple fields in a Redis hash with HMSET for key 'user:2' with fields 'name' as 'Bob' and 'age' as '25'.

A HMSET user:2 name Bob age 25

B HMSET user:2 {name: Bob, age: 25}

C HMSET user:2 [name Bob age 25]

D HMSET user:2 (name Bob, age 25)

💡 Hint

HMSET expects key followed by field and value pairs separated by spaces.

The correct syntax for HMSET is: HMSET key field1 value1 field2 value2 ... Option A follows this format exactly.

❓ optimization

advanced

Which approach is best to retrieve multiple fields efficiently?

You want to get the values of fields 'name', 'age', 'city', and 'email' from a Redis hash 'user:3'. Which command is the most efficient to retrieve all these fields at once?

A HGETALL user:3

B

HGET user:3 name
HGET user:3 age
HGET user:3 city
HGET user:3 email

C GET user:3

D HMGET user:3 name age city email

💡 Hint

HMGET retrieves multiple specified fields in one command.

HMGET is designed to get multiple fields in one call, making it more efficient than multiple HGET calls. HGETALL returns all fields but may return unnecessary data. GET is for string keys, not hashes.

🔧 Debug

advanced

Why does this HMGET command return null for one field?

Given these commands:

HMSET user:4 name "Eve" age "28"
HMGET user:4 name city

Why does the HMGET command return ["Eve", null]?

Redis

HMSET user:4 name "Eve" age "28"
HMGET user:4 name city

A The field 'city' does not exist in the hash, so HMGET returns null for it.

B The HMGET command syntax is incorrect, causing null to be returned.

C Redis hashes cannot store more than two fields, so 'city' is ignored.

D The HMSET command failed to set any fields, so all values are null.

💡 Hint

HMGET returns null for fields that do not exist in the hash.

Since 'city' was never set in the hash 'user:4', HMGET returns null for that field while returning the value for 'name'.

🧠 Conceptual

expert

What is the main difference between HMSET and HSET in recent Redis versions?

Redis introduced HSET to replace HMSET. What is the key difference between HMSET and HSET when setting multiple fields in a hash?

A HMSET supports setting fields with expiration, HSET does not.

B HMSET can set multiple fields but HSET can only set one field at a time.

C HSET can set multiple fields at once and HMSET is deprecated but both behave similarly.

D HSET requires JSON format for fields, HMSET uses plain key-value pairs.

💡 Hint

Check Redis documentation about HMSET deprecation and HSET enhancements.

In recent Redis versions, HMSET is deprecated. HSET now supports setting multiple fields at once, making it the preferred command.