I have a table `Products` with this content:

```
  | Product title | price | price_sales | new_price |
1 | Product A     | 100   | 80          | ???       |
2 | Product B     | 100   | 0           | ???       |
3 | Product C     | 400   | 200         | ???       |

```

I have to do an update query about all products: the column `new_price` has to be a column with **10% discount** on the current price. 
When there is no price\_sales (price\_sales = 0), the column `price` is the actual price.

The result has to be:

```
  | Product title | price | price_sales | new_price |
1 | Product A     | 100   | 80          | 76        |
2 | Product B     | 100   | 0           | 90        |
3 | Product C     | 400   | 200         | 180       |

```