Coalesce values in one column based on another column

Question

How do I coalesce values in a column grouped by another column?

e.g. How do I coalesce column 2 values by column 1 values? So turn the following:

Column 1|Column 2
-----------------
A       |Bob
A       |
B       |Mary
C       |
C       |Kevin
C       |
D       |
D       |

Into this:

Column 1|Column 2
-----------------
A       |Bob
B       |Mary
C       |Kevin
D       |

Thanks!

Answer 1

Use aggregation. Here is one way:

select col1, max(col2)
from t
group by col1;