HDEL for field removal in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Redis command HDEL do?

The HDEL command removes one or more fields from a hash stored at a key. It deletes the specified fields and returns the number of fields that were removed.

beginner

How do you remove multiple fields from a Redis hash using HDEL?

You list all the fields you want to remove after the key. For example: HDEL myhash field1 field2 removes both field1 and field2 from the hash myhash.

intermediate

What happens if you try to remove a field that does not exist in a Redis hash using HDEL?

If the field does not exist, HDEL simply ignores it and does not count it as removed. The command returns the number of fields actually removed.

beginner

Can HDEL remove fields from a key that does not exist in Redis?

Yes. If the key does not exist, HDEL returns 0 because there are no fields to remove.

beginner

What is the return value of HDEL?

It returns an integer representing how many fields were removed from the hash.

What does the Redis command HDEL myhash field1 do?

A Deletes the entire hash <code>myhash</code>

B Removes the field <code>field1</code> from the hash <code>myhash</code>

C Adds a new field <code>field1</code> to the hash <code>myhash</code>

D Returns the value of <code>field1</code> in <code>myhash</code>

HDEL removes specified fields from a hash. Here, it removes field1 from myhash.

If you run HDEL myhash field1 field2 and only field1 exists, what is the return value?

A An error

B 0

C 2

D 1

The command returns the number of fields actually removed. Since only field1 exists, it returns 1.

What happens if you use HDEL on a key that does not exist?

A It returns 0

B It creates the key

C It returns an error

D It removes all fields

If the key does not exist, HDEL returns 0 because there are no fields to remove.

Which data type does HDEL operate on in Redis?

A Hash

B List

C Set

D String

HDEL works on hashes, which are collections of field-value pairs.

Can HDEL remove fields from multiple hashes at once?

A Yes, by listing multiple keys

B Yes, but only if the hashes have the same fields

C No, it only works on one hash key at a time

D Yes, but only in Redis Cluster mode

HDEL removes fields from a single hash key per command.

Explain how the HDEL command works in Redis and what it returns.

Think about deleting parts of a dictionary in Redis.

Describe a real-life example where you might use HDEL in a Redis hash.

Imagine a user profile stored as a hash with many fields.