SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21a678d3e8f2e1fb0d096d97d5cf65e6520170b5574388086acf006ba78642d2' 
  AND token = 'zUhRdlP8WTzCJ+JobIYmIw2wnSg1GPzsKMPs3x8LxaE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00031

JSON explain

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