HSET and HGET for fields 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:

HSET user:1 name "Alice" age 30
HGET user:1 name

What will be the output of the HGET command?

Redis

HSET user:1 name "Alice" age 30
HGET user:1 name

A Alice

B nil

C 30

D Error: wrong type

💡 Hint

HSET stores fields and values in a hash. HGET retrieves the value of a given field.

The HSET command sets multiple fields in the hash 'user:1'. The field 'name' is set to 'Alice'. The HGET command retrieves the value of the 'name' field, which is 'Alice'.

❓ query_result

intermediate

What happens if you HGET a non-existing field?

Given the hash key user:2 with fields:
HSET user:2 name "Bob"

What is the result of:
HGET user:2 age?

Redis

HSET user:2 name "Bob"
HGET user:2 age

A nil

B "" (empty string)

C 0

D Error: field not found

💡 Hint

HGET returns nil if the field does not exist in the hash.

Since the field 'age' does not exist in the hash 'user:2', HGET returns nil to indicate no value.

📝 Syntax

advanced

Which command correctly sets multiple fields in a hash?

You want to set the fields 'name' to 'Carol' and 'age' to 25 in the hash 'user:3'. Which command is correct?

A HSET user:3 (name, Carol, age, 25)

B HSET user:3 name Carol age 25

C HSET user:3 [name, Carol, age, 25]

D HSET user:3 {name: Carol, age: 25}

💡 Hint

HSET takes the key followed by field and value pairs as separate arguments.

The correct syntax for HSET is: HSET key field1 value1 field2 value2 ... Option B follows this syntax exactly.

❓ optimization

advanced

Which approach is more efficient to update multiple fields in a Redis hash?

You need to update 5 fields in a Redis hash. Which is the best approach?

A Use HGET to get all fields, modify locally, then HSET all fields again

B Use 5 separate HSET commands, one per field

C Use one HSET command with all 5 field-value pairs at once

D Use multiple HGET commands, one per field, then HSET for each

💡 Hint

Minimizing the number of commands sent to Redis improves performance.

Using a single HSET command with all fields reduces network overhead and is more efficient than multiple commands.

🧠 Conceptual

expert

What is the result of this Redis command sequence?

Given the commands:
HSET user:4 name "Dave" age 40
HSET user:4 age 41
HGET user:4 age

What is the output of the last command?

Redis

HSET user:4 name "Dave" age 40
HSET user:4 age 41
HGET user:4 age

A "40"

B Error: field not found

C nil

D "41"

💡 Hint

HSET overwrites existing fields with new values.

The second HSET updates the 'age' field to 41, so HGET returns "41".