Question: I am using three tables and I am trying to calculate discounted price by using this. 

```
(Price.price - ccons.discountPrice - mcons.discountPrice) "Discount Price"

```

However, when one of value is null, Discount price displays "NULL". How can I resolve it? Can I declare NULL value is saying "0"? Or do you have any idea for this calculation?

Answer: 
```
Price.price - NVL(ccons.discountPrice, 0) - NVL(mcons.discountPrice, 0)

```
Most likely, you just want to wrap all three components in `NVL` functions, i.e.

```
nvl(Price.price,0) - 
  nvl(ccons.discountPrice,0) - 
  nvl(mcons.discountPrice,0) "Discount Price"

```

If some of those columns are declared to be `NOT NULL` (it would seem unlikely that `Price.price` could legitimately be `NULL`), you wouldn't need to `NVL` those columns.