SQL 查询 JOIN 和聚合

Question

SQL 的新手，谷歌搜索无果。这是架构：

                   "users"
       Column        |           Type           |          
---------------------+--------------------------+
 id                  | text                     |
 name                | text                     |
 title               | text                     |
 org_id              | text                     |
 type.               | text                     |




                         "organizations"
             Column             |           Type           |  
--------------------------------+--------------------------+
 id                             | text                     |
 name                           | text                     |



                "posts"
      Column       |           Type           |    
-------------------+--------------------------+
 id                | text                     |
 title             | text                     |
 content           | jsonb[]                  |
 owner_id          | text                     |
 org_id            | text                     |
 is_public         | boolean                  |

我的目标是在一个 table 中显示每个组织有多少私人主题、管理员和标准用户，如下所示：

   Org    | Users | Admins  | Private Posts 
----------+-------+-------+---------------
 Org1     |    56 | 10      |            22
 Org2     |   111 | 10      |            34

现在，我只得到这个：

   Org    | Count | Type  | Private Posts 
----------+-------+-------+---------------
 Org1     |    10 | admin |            22
 Org2     |   111 | user  |            34
 Org1     |    56 | user  |            22
 Org2     |    10 | admin |            34

使用：

SELECT t1.id as "Org", t1.cnt as "Count", t1.type as "Type", t2.cnt as "Private Posts" from
    (SELECT COUNT(u.type) as "cnt", u.type as "type", o.id FROM "users" AS u JOIN 
    "organizations" AS o ON o.id=u.org_id GROUP BY u.type, o.id) as t1 join
        (SELECT COUNT(org_id) as "cnt", org_id from posts WHERE is_public = False group 
        by org_id) as t2 on t2.org_id = t1.id;

我基本上尝试加入用户和组织并根据组织和用户类型（t1）进行计数，然后统计帖子（t2）中的 public 个帖子，并尝试根据加入 t1 和 t2组织 ID。感谢任何帮助。

Answer 1

考虑一个名为 条件聚合 的概念，它根据条件逻辑将结果转换为所需的宽格式列。 Postgres 为这种类型的查询维护有用的 FILTER，但也可以使用与其他 RDBMS 共享的 CASE 语句：

SELECT o.id AS "Org",
       COUNT(*) FILTER(WHERE u.type = 'user') AS "Users",
       COUNT(*) FILTER(WHERE u.type = 'admin') AS "Admins",
       COUNT(*) FILTER(WHERE is_public = False) AS "Private Posts"
FROM users u
JOIN organizations o 
   ON o.id = u.org_id
JOIN posts p 
   ON o.id = p.org_id
GROUP BY o.id;

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