### DAY 
```sql
DAY(expr)
```
####  Description

The `DAY` function is used to extract the day of the month from a given date or timestamp expression `expr`. This function works correctly for both date and timestamp types of data, returning an integer value that represents the day of the month.

#### Parameter Description

* `expr`: `date` or `timestamp_ltz` type, representing the input date or timestamp.

#### Return Result

Returns an integer representing the day of the month of the input date or timestamp.

#### Usage Example

1. Extract the day from a specific date:
   ```sql
   SELECT DAY('2022-03-31');
   +---------------------+
   | `DAY`('2022-03-31') |
   +---------------------+
   | 31                  |
   +---------------------+
   ```
The result will return 31, indicating that '2022-03-31' is the 31st day of March.

2. Extract the day from a timestamp and combine it with other operations:
   ```sql
   SELECT DAY(CURRENT_TIMESTAMP()) + 5 AS target_day;
   +------------+
   | target_day |
   +------------+
   | 26         |
   +------------
   ```
3. Compare two dates to determine if they are on the same day:
   ```sql
   SELECT (DAY('2022-03-31') = DAY('2022-03-01')) AS is_same_day;
   +-------------+
   | is_same_day |
   +-------------+
   | false       |
   +-------------+
   ```