HEXISTS for field check in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Check if a field exists in a Redis hash

Given a Redis hash named user:1000 with fields name and email, what is the output of the command HEXISTS user:1000 email?

Redis

HSET user:1000 name "Alice" email "[e-mail]"

A error

B 0

C nil

D 1

💡 Hint

HEXISTS returns 1 if the field exists, otherwise 0.

The HEXISTS command checks if a field exists in a hash. Since email is set, it returns 1.

❓ query_result

intermediate

Check non-existing field in Redis hash

What is the output of HEXISTS user:1000 age if the hash user:1000 only contains fields name and email?

Redis

HSET user:1000 name "Alice" email "[e-mail]"

A 1

B 0

C nil

D error

💡 Hint

Check if the field is present or not.

The field age does not exist in the hash, so HEXISTS returns 0.

📝 Syntax

advanced

Identify the correct HEXISTS command syntax

Which of the following commands correctly checks if the field status exists in the hash order:123?

A HEXISTS order:123 status

B HEXISTS status order:123

C HEXISTS order:123:status

D HEXISTS order:123 status extra

💡 Hint

The syntax is HEXISTS key field

The correct syntax is HEXISTS key field. Option A follows this format.

❓ query_result

advanced

HEXISTS behavior with non-hash key

What happens when you run HEXISTS mykey field1 if mykey is a string key with value hello?

Redis

SET mykey "hello"

A 1

B 0

C error

D nil

💡 Hint

HEXISTS only works on hashes.

If the key is not a hash, Redis returns a type error when running HEXISTS.

🧠 Conceptual

expert

Using HEXISTS in conditional logic

You want to increment a numeric field visits in a Redis hash page:home only if the field exists. Which Redis command sequence correctly achieves this?

A Use a Lua script to check HEXISTS and then HINCRBY

B HINCRBY page:home visits 1

C HEXISTS page:home visits && HINCRBY page:home visits 1

D IF HEXISTS page:home visits THEN HINCRBY page:home visits 1

💡 Hint

Redis commands are atomic but do not support IF statements directly.

Redis does not support IF statements in its command syntax. To conditionally increment a field only if it exists, you must use a Lua script that checks HEXISTS and then increments with HINCRBY atomically.