Postgresql 如何计算postgres中的多个连接行？

我有4张桌子：A、B、C、D

• 表B具有a的外键
• 表C有一个a的外键
• 表D有一个C的外键

到目前为止我可以查询的内容：

• 我知道如何从A中选择所有行，并计算B中连接行的数量
• 我知道如何从A中选择所有行，并从D（通过C）计算连接行的数量

现在我想将这两个查询合并到一个select中，并显示count_b和count_d。但是结果select显示了错误的计数。我是这样做的：

SELECT
  "A"."id",
  COUNT("B"."id") AS "B_count",
  COUNT("D"."id") AS "D_count"
FROM "users" AS "A" LEFT OUTER JOIN "B" AS "B"
    ON "A"."id" = "B"."a__id"
  LEFT OUTER JOIN "C" AS "C"
    ON "A"."id" = "C"."a_id"
  LEFT OUTER JOIN "D" AS "D"
    ON "C"."id" = "D"."c_id"
GROUP BY "A"."id"

---

分组方式可能存在问题。似乎我需要为每一个计数写单独的分组。我正在寻找没有嵌套选择的结果（因为我仍然需要将其映射到ORM，不要问为什么）。是否可以使用
distinct by
存档？
由于您要加入3个表，您应该在计数内使用distinct：

SELECT
  "A"."id",
  COUNT(DISTINCT "B"."id") AS "B_count",
  COUNT(DISTINCT "D"."id") AS "D_count"
FROM "users" AS "A" LEFT OUTER JOIN "B" AS "B"
    ON "A"."id" = "B"."a__id"
  LEFT OUTER JOIN "C" AS "C"
    ON "A"."id" = "C"."a_id"
  LEFT OUTER JOIN "D" AS "D"
    ON "C"."id" = "D"."c_id"
GROUP BY "A"."id"

尝试使用count（distinct D）和count（distinct B）我缺少的是distinct:-）