How can I remove unused data files from a Delta Lake table using Databricks SQL?
You can remove unused data files from a Delta Lake table using Databricks SQL by running the `REORG TABLE` command with the `APPLY (PURGE)` option. Here's an example:

```sql
REORG TABLE table_name APPLY (PURGE);
```

Replace `table_name` with the name of your Delta Lake table. This command rewrites files that contain soft-deleted data, such as the column data dropped by `ALTER TABLE DROP COLUMN`.

After running `APPLY (PURGE)`, the soft-deleted data may still exist in the old files. To physically delete the old files, you can run the `VACUUM` command.

Here's an example of how to vacuum a Delta Lake table:

```sql
VACUUM table_name;
```

Replace `table_name` with the name of your Delta Lake table. This command physically deletes the old files that contain soft-deleted data.

Note that `REORG TABLE` is idempotent, meaning that if it is run twice on the same dataset, the second run has no effect.