Combined 2 columns into one column SQL

Question

I'm a beginner to Postgres and need to do something like this. My Postgres query output has 2 columns. I need to combine these two like below.

Column 1:

A
B
C

Column 2:

D
D
D

Output Column:

A
B
C
D

(all values from column 1 and distinct values from column 2)

Is this possible in PostgreSQL?

Answer 1

Hi there is one fancy way:

select distinct unnest(array[
        column1
        , column2
    ])
from table

Answer 2

You need something like this :

 select  col    from (
   select Column1 as col   from <your table >
    union all 
    select distinct Column2 as col   from <your table>
) as myview order by col