可以使用聚合和窗口函数：

select col_1, col_2, col_3, col_4
from (
    select
        col_1, 
        col_2, 
        col_3, 
        col_4, 
        rank() over(partition by col_1 order by count(*) desc) rn
    from mytable t
    group by col_1, col_2, col_3, col_4
) t
where rn = 1

与 row_number() 窗口功能：

select t.col_1, t.col_2, t.col_3, t.col_4
from (
  select col_1, min(col_2) col_2, col_3, col_4,
    row_number() over (partition by col_1 order by count(*) desc) rn
  from tablename
  group by col_1, col_3, col_4
) t
where t.rn = 1

请看演示。
结果：

| col_1 | col_2 | col_3 | col_4 |
| ----- | ----- | ----- | ----- |
| a1    | b1    | c1    | d1    |
| a2    | b12   | c1    | d1    |
| a3    | b13   | c1    | d1    |

如果需要完整的行，可以使用窗口函数：

select t.*
from (select t.*,
             rank() over (partition by col1 order by cnt desc) as seqnum
      from (select t.*, count(*) over (partition by col1, col3, col4) as cnt
            from t
           ) t
     ) t
where seqnum = 1;

最里面的子查询统计每个col1/col3/col4组合的行数。中间的子查询枚举每个子查询中计数最高的行 col1 . 用于最高计数的最外层筛选器。