HGETALL for all fields in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of HGETALL on a hash with multiple fields?

Given a Redis hash stored as HSET user:1 name "Alice" age "30" city "Paris", what will HGETALL user:1 return?

Redis

HSET user:1 name "Alice" age "30" city "Paris"
HGETALL user:1

A {"name": "Alice", "age": "30", "city": "Paris"}

B ["user:1", "name", "Alice", "age", "30", "city", "Paris"]

C ["name", "Alice", "age", "30", "city", "Paris"]

D ["name", "Alice", "city", "Paris"]

💡 Hint

HGETALL returns a flat list of field and value pairs.

HGETALL returns an array of strings representing alternating fields and their values in the hash. It does not return a dictionary or include the key name.

🧠 Conceptual

intermediate

Understanding HGETALL output format

Why does HGETALL return a flat list of fields and values instead of a dictionary?

A Because Redis hashes are stored as sorted sets.

B Because Redis stores hashes internally as JSON objects.

C Because HGETALL only returns keys, not values.

D Because Redis protocol returns arrays of strings and clients parse them into key-value pairs.

💡 Hint

Think about how Redis communicates data over the network.

Redis protocol returns arrays of strings. The client interprets the alternating elements as field and value pairs to reconstruct the hash.

📝 Syntax

advanced

Which command correctly retrieves all fields and values from a Redis hash?

Select the correct Redis command to get all fields and values from the hash key session:123.

A HGET session:123 *

B HGETALL session:123

C GETALL session:123

D HMGET session:123

💡 Hint

Only one command is the official Redis command for this purpose.

HGETALL is the Redis command that returns all fields and values of a hash. GETALL and HMGET are invalid or incomplete commands.

❓ optimization

advanced

Optimizing retrieval of specific fields vs all fields

You want to retrieve only the fields name and email from a large Redis hash user:1000. Which approach is more efficient?

A Use <code>HMGET user:1000 name email</code> to get only needed fields.

B Use <code>HGETALL user:1000</code> and filter fields in the client.

C Use <code>GET user:1000</code> to get the whole hash as a string.

D Use <code>HKEYS user:1000</code> to get all keys then get values one by one.

💡 Hint

Fetching only needed data reduces network and processing load.

HMGET fetches only specified fields, reducing data transfer and client filtering compared to HGETALL.

🔧 Debug

expert

Why does HGETALL return an empty list?

You run HGETALL order:500 but get an empty list []. What is the most likely reason?

A The key <code>order:500</code> does not exist or is not a hash.

B HGETALL only works on strings, not hashes.

C Redis server is down and returns empty results.

D You need to run <code>HGETALL</code> with a pattern argument.

💡 Hint

Check if the key exists and its data type.

If the key does not exist or is not a hash, HGETALL returns an empty list. It does not accept patterns.