月底盘点，老板想知道店里一共有多少件东西。把 products 表里所有的 stock 加起来，结果只要一个数。
| id | name | category | price | stock |
|---|---|---|---|---|
| 1 | Milk tea | drink | 12 | 30 |
| 2 | Lemon water | drink | 8 | 50 |
| 3 | Cheesecake | cake | 25 | 6 |
| 4 | Cookie | snack | 5 | 80 |
| 5 | Brownie | cake | 18 | 0 |
| 6 | Iced coffee | drink | 15 | 20 |
| 7 | Chips | snack | 7 | 40 |
| 8 | Fruit tart | cake | 28 | 4 |
| id | name | category | price | stock |
|---|---|---|---|---|
| 1 | Milk tea | drink | 12 | 30 |
| 2 | Lemon water | drink | 8 | 50 |
| 3 | Cheesecake | cake | 25 | 6 |
| 4 | Cookie | snack | 5 | 80 |
| 5 | Brownie | cake | 18 | 0 |
| 6 | Iced coffee | drink | 15 | 20 |
| 7 | Chips | snack | 7 | 40 |
| 8 | Fruit tart | cake | 28 | 4 |
-- 在这里写：用 SUM 把 stock 加起来 SELECT stock FROM products;
写好了先点「运行」看看结果，没问题再点「提交」。