SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '76cba681063a028f66ce3a955a99509552a31d49ff0c2c36f6853612035f5b12' 
  AND token = 'SblaBVkXrw3pByUD1NfNofjxM0SaIhcXvTLpXnKnNn0=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00033

JSON explain

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