I want to get a subset of a table, here's the example:

```
1   A
2   A
3   B
4   B
5   C
6   D
7   D
8   D

```

I want to get the unique record, but with the smallest id:

```
1   A
3   B
5   C
6   D

```

How can I write the SQL in SQL Server? Thanks!