distinct is NOT a function. It always operates on all columns of the result.
The difference between
select distinct (foo), bar and
select distinct foo, bar is the same as the difference between
select (foo), bar and
select foo, bar. The paranthesis is just "noise".
When you write
select (foo,bar) you are actually creating an anonymous object type in Postgres which results in a single column that has two attributes - which is not what you actually want.
As you are using Postgres, you can use the Postgres specific extension
DISTINCT ON which - in contrast to the standard
DISTINCT does operate on a sub-set of the columns.
You have to specfiy an ORDER BY in that case to "define" which of the rows to take if there is more than one with the same combination of
CREATE TABLE new_name
SELECT DISTINCT ON (table.field1, table.field2),
ORDER BY ..
If you want to stick to ANSI SQL you will need a window function for this:
create table new_name
select column1, column2, column3, column4, column5, column6
select column1, column2, column3, column4, column5, column6,
row_number() over (partition by column1, column2 order by ...) as rn
where rn = 1;
For a large table
DISTINC ON is probably faster than the solution with the window function.