SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '251899f77bd68f4d8b31768a4462c2346f7c815284f414f301473c3b3cd8e049' 
  AND token = 'UC/kWGXoxK41NwBGCczYqXSrYevJeJwj5pyV5k3RNW4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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