sql - group by 后将多行合并为一行

Question

更新: https://www.db-fiddle.com/f/5fGUTSsAhGRPYPk33wDSzz/0

很抱歉提出了与上一个问题非常相似的问题，但我真的被困在这里了。

有多个表:

• 项目 → items_roles → 角色
• 项目 → 区域 → roles_zones → 角色

结构:

• 项目:id，zone_id
• items_roles: role_id, item_id
• 区域:id
• roles_zones: role_id, zone_id
• 角色:id，role_type_id，

我正在尝试向项目添加角色字段，它应该采用 role_type 并且它是来自 items_zones 的值，如果它是 NULL，则从区域 (roles_zones) 获取回退值。

我开始于:

SELECT 
    items.id,
    (z_roles.role_type_id) as z_role_type_id,
    (z_roles.id) as z_role_id,
    MAX(i_roles.role_type_id) as i_role_type_id,
    MAX(i_roles.id) as i_role_id
FROM 
    items
LEFT JOIN 
    zones as j_zones ON j_zones.id = items.zone_id
LEFT JOIN 
    roles_zones ON roles_zones.zone_id = j_zones.id
LEFT JOIN 
    roles as z_roles ON (z_roles.id = roles_zones.role_id)
LEFT JOIN 
    items_roles ON items_roles.item_id = items.id
LEFT JOIN 
    roles as i_roles ON items_roles.role_id = i_roles.id
                     AND (z_roles.role_type_id = i_roles.role_type_id)
WHERE 
    items.id = 834
GROUP BY
    items.id, z_roles.role_type_id, z_roles.id
ORDER BY 
    i_role_id;

看起来不错:

id  |z_role_type_id |z_role_id |i_role_type_id |i_role_id |
----+---------------+----------+---------------+----------+
834 |5              |111       |5              |68        |
834 |11             |120       |11             |120       |
834 |7              |77        |               |          |
834 |2              |2         |               |          |
834 |12             |91        |               |          |
834 |4              |78        |               |          |
834 |8              |36        |               |          |

现在这个查询:

SELECT
    items.id,
    z_roles.role_type_id as z_role_type_id,
    z_roles.id as z_role_id,
    MAX(i_roles.role_type_id) AS i_role_type_id,
    MAX(i_roles.id) AS i_role_id,
    MAX(CASE
           WHEN (i_roles.role_type_id = 5) THEN i_roles.id
           WHEN (z_roles.role_type_id = 5) THEN z_roles.id
        END) AS role_type_5_value,
    MAX(CASE
           WHEN (i_roles.role_type_id = 11) THEN i_roles.id
           WHEN (z_roles.role_type_id = 11) THEN z_roles.id
        END) AS role_type_11_value,
    MAX(CASE
           WHEN (i_roles.role_type_id = 7) THEN i_roles.id
           WHEN (z_roles.role_type_id = 7) THEN z_roles.id
        END) AS role_type_7_value
FROM 
    items
LEFT JOIN 
    zones AS j_zones ON j_zones.id = items.zone_id
LEFT JOIN 
    roles_zones ON roles_zones.zone_id = j_zones.id
LEFT JOIN 
    roles AS z_roles ON (z_roles.id = roles_zones.role_id)
LEFT JOIN 
    items_roles ON items_roles.item_id = items.id
LEFT JOIN 
    roles AS i_roles ON items_roles.role_id = i_roles.id
                     AND (z_roles.role_type_id = i_roles.role_type_id)
WHERE 
    items.id = 834
GROUP BY 
    items.id,
    z_roles.role_type_id,
    z_roles.id
ORDER BY 
    items.id, i_role_id;

生成这个:

 id  | z_role_type_id | z_role_id | i_role_type_id | i_role_id | role_type_5_value | role_type_11_value | role_type_7_value 
-----+----------------+-----------+----------------+-----------+-------------------+--------------------+-------------------
 834 |              5 |       111 |              5 |        68 |               111 |                    |                  
 834 |             11 |       120 |             11 |       120 |                   |                120 |                  
 834 |              7 |        77 |                |           |                   |                    |                77
 834 |              2 |         2 |                |           |                   |                    |                  
 834 |             12 |        91 |                |           |                   |                    |                  
 834 |              4 |        78 |                |           |                   |                    |                  
 834 |              8 |        36 |                |           |                   |                    |                  
(7 rows)

role_type_5_value 有多行且值错误。可能是因为 MAX 聚合器。是否可以使用类似 first 聚合器的东西(因为按 i_role_id 排序的行和第一个结果是正确的)？

我想要这个:

 id  | role_type_5_value | role_type_11_value | role_type_7_value 
-----+-------------------+--------------------+-------------------
 834 |                68 |                120 |                77    

我试图通过聚合字段分组依据，(role_type_5_value, role_type_11_value, role_type_7_value) 但这是根本不起作用。

Answer 1

首先:从主查询中删除不需要的桥接表并将它们压缩到 EXISTS() 项中将简化您的查询。(您只需要三个表，其余的是胶水)

其次:不要将所有术语都放在 GROUP BY 子句中。

---

SELECT
  i0.id
   , MAX(CASE
    WHEN (r1.role_type_id = 5) THEN r1.id
    WHEN (r0.role_type_id = 5) THEN r0.id
  END) AS role_type_5_value
  , MAX(CASE
    WHEN (r1.role_type_id = 11) THEN r1.id
    WHEN (r0.role_type_id = 11) THEN r0.id
  END) AS role_type_11_value
  , MAX(CASE
    WHEN (r1.role_type_id = 7) THEN r1.id
    WHEN (r0.role_type_id = 7) THEN r0.id
  END) AS role_type_7_value

FROM items i0
LEFT JOIN roles AS r0
  ON EXISTS ( SELECT*
        FROM zones AS z0
        JOIN roles_zones rz ON rz.zone_id = z0.id
        WHERE z0.id = i0.zone_id
        AND r0.id = rz.role_id)

LEFT JOIN roles AS r1
  ON EXISTS ( SELECT*
        FROM items_roles ir
        WHERE ir.item_id = i0.id
        AND ir.role_id = r1.id
        AND r0.role_type_id = r1.role_type_id
        )

WHERE i0.id = 834
GROUP BY i0.id
         -- r0.role_type_id,
         -- r0.id
ORDER BY i0.id;