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EXISTS

Checks if the specified key exists in the Redis database.

Syntax​

EXISTS key [key ...]

Parameters​

  • key: One or more keys to check for existence. Each key is specified separately.

Details​

  • Available since: 1.0.0
  • Time complexity: O(1) for each key checked.
  • ACL categories: @read

The EXISTS command determines whether one or more keys exist in the Redis database. It returns 1 if the key exists and 0 if it does not. The command can accept multiple keys and will return an integer array indicating the existence of each key.

Examples​

Checking a Single Key​

To check if a single key exists:

EXISTS mykey

This command will return 1 if the key mykey exists, or 0 if it does not.

Checking Multiple Keys​

To check if multiple keys exist:

EXISTS key1 key2 key3

This command will return an array of integers, where each integer corresponds to the existence status of each key:

1) (integer) 1
2) (integer) 0
3) (integer) 1

In this example, key1 and key3 exist, while key2 does not.

Using EXISTS for Key Management​

  1. Create keys:

    SET key1 "value1"
    SET key2 "value2"

  2. Check existence:

    EXISTS key1 key2 key3

The result will indicate the presence of key1 and key2, and 0 for key3, which does not exist.

RESP2/RESP3 Reply​

  • Integer reply: 1 if the key exists, 0 if it does not. For multiple keys, an array of integers is returned.

Example Reply​

If checking multiple keys:

1) (integer) 1
2) (integer) 0
3) (integer) 1

This means key1 and key3 exist, while key2 does not.

Notes​

  • The EXISTS command can be used to verify the presence of keys before performing operations that assume the key exists.
  • In Redis versions 3.0.0 and above, the EXISTS command is more efficient with multiple keys, returning an array of results in a single call.
  • For checking the existence of keys that may be set to expire, ensure you perform checks at appropriate intervals.