EXISTS to check key existence in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Redis command EXISTS do?

The EXISTS command checks if a given key exists in the Redis database. It returns 1 if the key exists, and 0 if it does not.

intermediate

How do you check multiple keys at once with EXISTS in Redis?

You can pass multiple keys to EXISTS. It returns the number of keys that exist among those given.

beginner

What is the return type of the EXISTS command in Redis?

It returns an integer: 1 if the key exists, 0 if it does not. When checking multiple keys, it returns the count of existing keys.

beginner

If you run EXISTS mykey and the key does not exist, what will Redis return?

Redis will return 0, indicating the key mykey does not exist.

beginner

Why is using EXISTS useful before performing operations on a key?

It helps avoid errors or unnecessary work by confirming the key is present before trying to read or modify it.

What does the Redis command EXISTS mykey return if mykey is present?

A 1

B 0

C null

D error

EXISTS returns 1 if the key exists.

How does EXISTS behave when checking multiple keys?

A Returns a list of keys that exist

B Returns 1 if all keys exist

C Returns 0 if any key is missing

D Returns the count of keys that exist

EXISTS returns the number of keys that exist among those checked.

Which of these is a valid use of EXISTS?

A EXISTS(key1, key2, key3)

B EXISTS key1, key2, key3

C EXISTS key1 key2 key3

D EXISTS [key1 key2 key3]

Redis EXISTS accepts multiple keys separated by spaces.

If EXISTS returns 0, what does it mean?

A No keys exist

B Command failed

C At least one key exists

D All keys exist

A return of 0 means none of the keys exist.

Why might you check key existence with EXISTS before deleting a key?

A To avoid deleting a key twice

B To confirm the key is present before deleting

C To rename the key

D To get the key's value

Checking existence helps avoid errors or unnecessary commands.

Explain how the Redis EXISTS command works and what it returns when checking one or multiple keys.

Think about how you check if something is there or not.

Describe a practical situation where using EXISTS before another Redis command is helpful.

Imagine you want to be sure before you act.