使用case转换employee值，并对转换后的值进行分组：

SELECT 
    CASE WHEN employee = 'a' THEN 'a' ELSE 'rest' END as e,
  SUM(amount) as a
FROM
  t
GROUP BY
  CASE WHEN employee = 'a' THEN 'a' ELSE 'rest' END

您也可以使用union：

SELECT 
  MAX(emlpoyee) as e,
  SUM(amount) as a
FROM
  t
WHERE employee = 'a'

UNION ALL

SELECT 
  'rest' as e,
  SUM(amount) as a
FROM
  t
WHERE employee <> 'a'

后一种方法可能会更占用资源，但可能更易于理解和维护，因此您需要判断您是看重直接的性能还是对开发人员友好(对于一个每天对100名员工运行一次的查询，你可以说让查询更容易理解会更好。对于一个每秒访问数万名员工的查询，性能应该优先）

请使用下面的查询，

select sum(amount), employee from
(select 
amount, case when employee = 'a' then employee else 'Rest' end as employee
from table t) t1
group by employee;

使用 case 表达式 group by 密钥：

select (case when employee = 'a' then employee else 'rest' end) as employee,
       sum(amount)
from t
group by (case when employee = 'a' then employee else 'rest' end) ;

这是一把小提琴(这碰巧使用mysql，但这是标准sql，可以在任何数据库中使用。）