I have table with values as 

```

    ColumnA   ColumnB

    ASD       A
    CSD       B
    DSD       C
    ESD       D
    FSD       D
    GSD       D

```

Column A is primary key, I need result as 

```

    ColumnA   ColumnB

    ASD       A
    CSD       B
    DSD       C
    ESD       D

```

I want all unique values from column B & their associated first values columnA.

I tried few queries & looked on Google but couldn't find ant solution .

Thanks,
Rohit.