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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '9d7578d558e402e4ba6ab9781d5f9991c91d72d091db20b90f4126eca2edb991' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00019

Explain
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE								Impossible WHERE noticed after reading const tables