考虑使用 filter aggreagate函数的语法，这是标准sql，postgres支持：

select 
    count(*) filter(where "exerciseType" = 'ROOT'   ) as total_root_exercises,
    count(*) filter(where "exerciseType" = 'DYNAMIC') as total_Dynamic_exercises,
    count(*) filter(where "exerciseType" = 'TEST'   ) as total_test_exercises 
FROM exer

如果你写这篇文章时没有 filter 语法（与第一次尝试一样），可移植语法是：

select 
    sum(case when "exerciseType" = 'ROOT'    then 1 else 0 end) as total_root_exercises,
    sum(case when "exerciseType" = 'DYNAMIC' then 1 else 0 end) as total_Dynamic_exercises,
    sum(case when "exerciseType" = 'TEST'    then 1 else 0 end) as total_test_exercises 
FROM exer

你可以用 filter 对于条件聚合：

SELECT count(*) filter (where "exerciseType" = 'ROOT') as total_root_exercises, 
       count(*) filter (where "exerciseType" = 'DYNAMIC') as total_dynamic_exercises,
       count(*) filter (where "exerciseType" = 'TEST') as total_test_exercises
FROM exer ;

您不需要外部聚合，但可以更简单地以行而不是列的形式返回结果：

select "exerciseType", count(*)
from exer
group by "exerciseType";

注意：我强烈反对使用转义列名。定义表时不要使用双引号，也不要在查询中使用双引号。