How can I modify all unmatched rows using the merge command in Delta Lake?
To modify all unmatched rows using the `merge` command in Delta Lake, you can use the `whenNotMatchedInsert` clause (in Scala and Python) or the `INSERT` clause (in SQL) to specify the values or expressions to use for the unmatched rows.

Here's an example of how to modify all unmatched rows using the `merge` command in Delta Lake with Python:
```python
from delta.tables import *

deltaTablePeople = DeltaTable.forPath(spark, '/tmp/delta/people-10m')
deltaTablePeopleUpdates = DeltaTable.forPath(spark, '/tmp/delta/people-10m-updates')

dfUpdates = deltaTablePeopleUpdates.toDF()

deltaTablePeople.alias('people') \
   .merge(
        dfUpdates.alias('updates'),
        'people.id = updates.id'
    ) \
   .whenMatchedUpdate(set = {
        "id": "updates.id",
        "firstName": "updates.firstName",
        "middleName": "updates.middleName",
        "lastName": "updates.lastName",
        "gender": "updates.gender",
        "birthDate": "updates.birthDate",
        "ssn": "updates.ssn",
        "salary": "updates.salary"
    }) \
   .whenNotMatchedInsert(values = {
        "id": "updates.id",
        "firstName": "updates.firstName",
        "middleName": "updates.middleName",
        "lastName": "updates.lastName",
        "gender": "updates.gender",
        "birthDate": "updates.birthDate",
        "ssn": "updates.ssn",
        "salary": "updates.salary"
    }) \
   .execute()
```
In this example, the `whenNotMatchedInsert` clause is used to specify the values to use for the unmatched rows. You can modify this clause to specify the values or expressions that you want to use for the unmatched rows.

Similarly, here's an example of how to modify all unmatched rows using the `merge` command in Delta Lake with SQL:
```sql
MERGE INTO people10m
USING people10mupdates
ON people10m.id = people10mupdates.id
WHEN MATCHED THEN UPDATE SET id = people10mupdates.id, firstName = people10mupdates.firstName, middleName = people10mupdates.middleName, lastName = people10mupdates.lastName, gender = people10mupdates.gender, birthDate = people10mupdates.birthDate, ssn = people10mupdates.ssn, salary = people10mupdates.salary
WHEN NOT MATCHED THEN INSERT (id, firstName, middleName, lastName, gender, birthDate, ssn, salary) VALUES (people10mupdates.id, people10mupdates.firstName, people10mupdates.middleName, people10mupdates.lastName, people10mupdates.gender, people10mupdates.birthDate, people10mupdates.ssn, people10mupdates.salary)
```
In this example, the `INSERT` clause is used to specify the values to use for the unmatched rows. You can modify this clause to specify the values or expressions that you want to use for the unmatched rows.