SQL & PL/SQL

Hi

I have a table like in below. I want to get max value at col6 using col1 as group by when it is 0. My sql syntax like in below but didn't work. I have no idea about using max and group by function at case/when  area if this is possible please suggest me what i am missing

Thank you

Database Version

11.2.0.3

Query

SELECT

        col1

       ,col2

       ,col3

       ,col4

       ,col5

       , case when 0 

    then (select max(col6) from MYTABLE group by col1)

    else col6

    end as  col6  

       ,[col7]

   FROM MYTABLE;

Sample Data

create table mytable (col1 number,col2 number,col3  number,col4 number,col5 number,col6 number,col7 number);

insert into mytable values (10639,2,2017,1,0.823,0,0.823);

insert into mytable values (10639,3,2017,1,0.798,0,0.798);

insert into mytable values (10639,4,2017,2,0.825,0.798,0.825);

insert into mytable values (10876,1,2017,1,0.826,0,0.826);

insert into mytable values (10876,2,2017,1,0.798,0,0.798);

insert into mytable values (10876,3,2017,1,0.828,0,0.828);

insert into mytable values (10876,4,2017,2,1,0.825,1);

insert into mytable values (11471,1,2017,1,0.792,0,0.792);

insert into mytable values (11471,2,2017,1,0.793,0,0.793);

insert into mytable values (11471,3,2017,1,0.794,0,0.794);

insert into mytable values (11471,4,2017,2,0.798,0.798,0.798);

insert into mytable values (11583,1,2017,1,0.796,0,0.796);

insert into mytable values (11583,2,2017,1,0.797,0,0.797);

insert into mytable values (11583,3,2017,1,0.798,0,0.798);

insert into mytable values (11583,4,2017,2,0.799,0.798,0.799);

insert into mytable values (11650,1,2017,1,0.826,0,0.826);

insert into mytable values (11650,2,2017,1,0.827,0,0.827);

insert into mytable values (11650,3,2017,1,0.828,0,0.828);

insert into mytable values (11650,4,2017,2,0.798,0.798,0.798);

Expected Output