Question

我有一条SQL语句：

SELECT
  p.id
  ,SUM(CASE WHEN pf.facility_code in ('S','H','E') then 1 ELSE 0 END) as facility_count
FROM people p
  inner JOIN people_facilities pf ON p.ID = pf.ID
group by p.id

从上面的陈述中，您将了解到facility_count不能大于3。但是，列表中的第一个有18个设施。

我指的是count with case and list

为什么这个计数不起作用？

Answer 1

如果要计算个不同工具的数量，请使用count(distinct)：

SELECT p.id,
       COUNT(DISTINCT CASE WHEN pf.facility_code in ('S','H','E') THEN pf.facility_code END) as facility_count
FROM people p JOIN
     people_facilities pf
     ON p.ID = pf.ID
GROUP BY p.id;

您的查询可疑。我希望JOIN更像pf.PeopleID = p.id。

如果没有，则可以通过删除JOIN来简化此查询，因为您要汇总的ID在people_facilities表中。我还怀疑条件可以移至WHERE子句：

SELECT pf.id, COUNT(DISTINCT pf.facility_code) as facility_count
FROM people_facilities pf
WHERE pf.facility_code IN ('S', 'H', 'E')
GROUP BY pf.id;

Answer 2

联接后，可能存在多个行，这些行具有相同的id和相同的facility_code。
因此，首先获取这些列的不同对，然后进行分组和汇总：

SELECT
  t.id,
  SUM(CASE WHEN t.facility_code in ('S','H','E') then 1 ELSE 0 END) as facility_count
FROM (
  SELECT DISTINCT p.id, pf.facility_code
  FROM people p inner JOIN people_facilities pf 
  ON p.ID = pf.ID
) t
group by t.id

设施计数不使用清单

2 个答案: