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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '538e81944f4d831b9f52a636c0fe2cfd84a2616a50dbaa5918bbd6d353969692' 
  AND token = 'Fp6TFZiWsP7AxzQeHUxWLKMrdTAsNrn4saQv1/U/A9k=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00015

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