可能要加上條件判斷 select (a.s1-b.s1) as s1相減 from a as a,b as b where a.sqid=b.sqid
你仔細看最後他有說 After these steps you can visit http://localhost:8080 . You can login...
其實什麼都不用灌React Online PlaygroundsReact installation
{} 可以換成自己的物件 var debug = Object.assign({},window.console);