How can I use the Databricks SQL `trunc` function to truncate a date to the first day of the month?
You can use the Databricks SQL `trunc` function to truncate a date to the first day of the month by using the 'MONTH', 'MM', or 'MON' unit. Here's an example:

```sql
SELECT trunc('2023-12-15', 'MONTH');
```

This will return the date `2023-12-01`, which is the first day of the month for the original date `2023-12-15`.