SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '255a235e6f590419bdb06c967466a876e22985beb7e0ebba532a10a14c633825' 
  AND token = 'Z3gdiDfIO0kMtLZTQ82bOYf0kn949MVbyrCFTEjmQRo=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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