EXISTS

EXISTS

Introduction and Use Case(s)

The EXISTS command in Redis is used to determine if one or more keys exist in the database. This command is commonly used to check the presence of keys before performing operations that depend on their existence, such as conditional updates or deletions.

Syntax

EXISTS key [key ...]

Parameter Explanations

key: One or more keys for which the existence needs to be checked. Multiple keys can be provided separated by spaces.

Return Values

The command returns an integer representing the number of keys that exist among the ones specified.

Example outputs:

(integer) 0: None of the specified keys exist.
(integer) 1: One of the specified keys exists.
(integer) N: N keys exist among the specified keys.

Code Examples

dragonfly> SET key1 "value1"
OK
dragonfly> EXISTS key1
(integer) 1
dragonfly> EXISTS key2
(integer) 0
dragonfly> EXISTS key1 key2 key3
(integer) 1
dragonfly> SET key2 "value2"
OK
dragonfly> EXISTS key1 key2 key3
(integer) 2

Best Practices

Combine EXISTS with other commands to implement logic that depends on the presence or absence of keys.
When checking multiple keys, understand that using EXISTS will return the count of existing keys which can be efficiently used to manage resources or make decisions.

Common Mistakes

Providing no keys. The command requires at least one key.
Misunderstanding the return value. The command returns the count of existing keys, not a boolean indicating if all specified keys exist.

FAQs

What happens if I check for the same key multiple times in the `EXISTS` command?

Each occurrence of the key is counted separately. For instance, EXISTS key1 key1 key2 will return 2 if key1 exists, regardless of whether key2 exists or not.