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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a3588fcc688b80c7e870913fe5d81a54879ec6cf6a56342ee5851be4a9e71a31' 
  AND token = 'PDXo7SLt1hi3fg8y4JnObfpxLZkSaD+KS51Aim6SsvA=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}