SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '5ae79d6a771a3b04f1e7254a9b3a860a5887e83394039e9e928a820f1b552037' 
  AND token = 'zR7ugAAzGBCCrRC7xXPfIKP9iSzy36DlHdZ+GQKqgYM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

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