MySQL和多個表

Question

我有三張桌子。

result: result_id, person_id, result
area: person_id, district_id
district:  province_id, district_id

我想要SUM(result.result) GROUP BY province_id

但是由於area.person_id具有多個person_id因此當我SUM(result.result)時，我SUM(result.result)得到兩倍的結果或三倍的值，從而增加了area.person_id中的area.person_id 。

你能幫忙嗎。

Answer 1

使用帶有DISTINCT的子查詢刪除重復項。

SELECT province_id, SUM(result)
FROM (
  SELECT DISTINCT d.province_id, r.person_id
  FROM result AS r
  JOIN area AS a ON r.person_id = a.person_id
  JOIN district AS d ON a.district_id = d.district_id) AS p
JOIN result AS r ON p.person_id = r.person_id
GROUP BY province_id

DEMO