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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c9b1b9dbf35549b11f8ba40c87148b8c91c3235f8e55ccf5d6ae8d43bc08a369' 
  AND token = 'U5Ar//sJBxpkUbA5ZtgSx1tyPjQhhds5Ys7421uMOWQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

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