结果取决于行的顺序。SQL表表示 * 无序 * 集，因此您无法对现有数据做任何您想要做的事情。
假设你有一个指定排序的列，你可以做：

select (case when row_number() over (partition by cms_code order by <ordering col< = 1
             then cms_code
        end) as cms_code, product_code
from t
order by cms_code, <ordering col>;

如果没有排序列，您还可以执行以下操作：

with cte as (
      select t.*, row_number() over (partition by cms_code order by cms_code) as seqnum
      from t
     )
select (case when seqnum = 1 then cms_code end) as cms_code,
       product_code
from t
order by cms_code, seqnum;

在这两种情况下，您都需要在外部查询中使用order by来保证结果集是有序的，因此“第一”行具有cms_code。

你可以使用窗口函数来对行进行编号，并将后续的值设置为null，只保留第1行的cms_code。

select 
  case 
    when row_number() over (partition by cms_code) = 1 then cms_code 
    else null 
  end cms_code
, product_code
from my_table
order by cms_code

我假设你希望cms_code的所有值都为null，它在第一个值之后是相同的。如果我错了，请纠正我下面的查询可以用于相同的：

SELECT 
  CASE
    WHEN ROW_NUMBER() OVER(PARTITION BY cms_code order by product) = 1 
    THEN NULL 
    ELSE cms_code 
  END AS cms_code,product 
FROM table;