SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '4b3711bcc246396135b62c028544e1813945ff0649dab3337401bc175199a11f' 
  AND token = 'MNvBBSMP1PaFWKTzVSnvFRyy1H56RUCALVMPqULF7cc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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