### ADD_DAYS Function
#### Function Description
The `ADD_DAYS` function is used to add `numDays` days to the given date `startDate`, returning a new date. If the result exceeds the date range supported by the system, it returns `null`.

#### Function Syntax
```
add_days(startDate, numDays)
```
#### Parameter Description
- `startDate`: Date type, represents the start date.
- `numDays`: Integer type, represents the number of days to add.

#### Return Result
Returns a new date of type `date`.

#### Usage Example
1. Add 5 days to the specified date:
```
SELECT add_days('2022-01-01', 5);
```
Results:
```
2022-01-06
```
2. Subtract 10 days from a specified date:
```
SELECT add_days('2022-01-15', -10);
```
Results:
```
2022-01-05
```
3. Calculate the important meeting date 100 days later:
```
SELECT add_days('2022-03-01', 100);
```
Results:
```
2022-06-09
```
4. Calculate the end date 200 days after the start date of a certain project:
```
SELECT add_days('2022-01-20', 200);
```
Results:
```
2022-08-18
```
#### Notes
- Ensure that the `startDate` parameter is in a valid date format, otherwise the function will return `null`.
- When the added days cause the date to exceed the system's supported range, the function will return `null`. Please check the return value.

By using the `ADD_DAYS` function, you can easily calculate future or past dates, providing great convenience when dealing with date-related issues.