### DAYOFMONTH 
#### Introduction
The `DAY` function is used to extract and return the day of the month from a given date expression (`date` or `timestamp_ltz` type), with the result being an integer.

#### Syntax
```
dayofmonth(expr)
```
#### Parameters
- `expr`: The date or time expression from which the days need to be extracted. It can be in formats such as string, timestamp, etc.

#### Return Result
Returns an integer representing the number of days in the month of the input expression.

#### Usage Example
1. Extract days from a string type date:
```
SELECT dayofmonth('2022-03-31'); -- Result: 31
```
2. Extract the number of days from the current timestamp:
```
SELECT dayofmonth(TIMESTAMP_LTZ '2022-08-15 03:21:00'); -- Result: 15
```
3. Extract days from a string-type timestamp:
```
SELECT dayofmonth('2022-09-01 10:30:20'); -- Result: 1
```
4. Extract and add the prefix "000" from the current timestamp:
```
SELECT '000' || dayofmonth(TIMESTAMP_LTZ '2022-10-20 14:45:30'); -- Result: 00020
```
#### Notes
- Ensure that the input date or time expression format is correct, otherwise, the function may not execute properly.
- When handling string-type time expressions, please ensure that the string format matches the format supported by the database.

By using the `DAY` function, you can easily extract the day from different types of date expressions for further date calculations or data display.