HEXISTS

HEXISTS is a command in Redis that checks whether a specified field exists within a hash stored at a given key. It is used to determine the presence of a field without retrieving its value.

Syntax: HEXISTS key field

Return value: An integer reply of 1 if the field exists in the hash, and 0 if it does not. If the key does not exist, the result is 0. If the key exists but is not a hash, the command returns a wrong type error.

Example: If a hash stored at key "user:1000" contains fields "name" and "email", HEXISTS user:1000 email would return 1, while HEXISTS user:1000 age would return 0.

Performance: HEXISTS operates in constant time, O(1), regardless of the size of the hash.

Notes: HEXISTS only checks for field existence; it does not return the field's value. If the key exists but is not a hash, Redis raises a WRONGTYPE error. This command is commonly used to conditionally perform further hash operations or to avoid unnecessary data retrieval.