Postgres不支持count()多于一列。但是，您可以使用以下类似的方法将两列简单地转换为匿名记录类型(col_one, col_two)的单列：-这是匿名记录类型的单列。
select COUNT(DISTINCT (person.id,(CASE WHEN salary_person.rating = 'Satisfactory' THEN 1 END))) AS totalSatisfactory,
COUNT(DISTINCT (person.id,(CASE WHEN salary_person.rating = 'Unsatisfactory' THEN 1 END))) AS totalUnsatisfactory
from person
join salary_person on person.id = salary_person.person_id;
注意两列的括号。
但是，在Postgres中，通过在filter子句中使用条件聚合，您可以采用一种更优雅的方式来执行所需的操作：
select COUNT(DISTINCT person.id) filter (where salary_person.rating = 'Satisfactory') AS totalSatisfactory,
COUNT(DISTINCT person.id) filter (where salary_person.rating = 'Unsatisfactory') AS totalUnsatisfactory
from person
join salary_person on person.id = salary_person.person_id;
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