SQL- 查询具有引用其他外键字段的外键字段的 table
SQL-Query for a table with a foreign-key-field that references other foreign-key-fields
我的数据库中有以下 table 的结构：
[table workers]
ID [PK] | worker | combined [FK]
--------+--------+--------------+
1 | John | 2
--------------------------------+
2 | Adam | 1
[table combined]
ID [PK] | name | helper [FK]
--------+----------------------+
1 | name1 | 1
2 | name2 | 2
[table helper]
ID [PK] | department [FK] | location [FK]
--------+-------------+-------------------
1 | 2 | 3
2 | 1 | 1
[table departments]
ID [PK] | department
--------+-------------+
1 | Development |
2 | Production |
[table location]
ID [PK] | department
--------+--------------+
1 | Paris |
2 | London |
3 | Berlin |
table "workers" 有一个外键字段 ("combined")。 table "combined" 有一个字段名和一个外键字段 "helper"，它又是一个带有两个外键字段的 table。
我现在的问题是，什么是最简单的SQL-查询得到以下table：
[table workers]
ID [PK] | worker | combined-Name| department | location
--------+--------+--------------+------------+-----------
1 | John | name2 | Development| Paris
--------------------------------+------------+-----------
2 | Adam | name1 | Production | Berlin
我已经用一些 LEFT-JOINS 尝试过，但没能成功地将所有 "clearnames" 连接到 table "workers"
此查询有效：
SELECT w.ID, worker, c.name AS `combined-Name`, d.department, l.department as
location FROM workers w
LEFT JOIN combined c ON c.ID = w.combined
LEFT JOIN helper h ON h.ID = c.helper
LEFT JOIN departments d ON d.ID = h.department
LEFT JOIN location l ON l.ID = h.location
GROUP BY w.ID
我使用 AS 关键字将名称设置为您的首选输出。
这是使用提供的结构和数据在本地测试的。
它基本上是 4 个简单的左连接，然后 select 不是 select 外部表的名称列而是 ID 的 select。
引用c.name上的别名是因为我们需要转义特殊字符-
使用以下查询：
select [workers].worker,[combined].name as combined-name,[departments].name as department,[location].name as location from [workers]
left join [combined] on [workers].combined = [combined].combined
left join [helper] on [helper].ID = [combined].helper
left join [departments] on [departments].ID = [helper].department
left join [location] on [location].ID = [helper].location
我的数据库中有以下 table 的结构：
[table workers]
ID [PK] | worker | combined [FK]
--------+--------+--------------+
1 | John | 2
--------------------------------+
2 | Adam | 1
[table combined]
ID [PK] | name | helper [FK]
--------+----------------------+
1 | name1 | 1
2 | name2 | 2
[table helper]
ID [PK] | department [FK] | location [FK]
--------+-------------+-------------------
1 | 2 | 3
2 | 1 | 1
[table departments]
ID [PK] | department
--------+-------------+
1 | Development |
2 | Production |
[table location]
ID [PK] | department
--------+--------------+
1 | Paris |
2 | London |
3 | Berlin |
table "workers" 有一个外键字段 ("combined")。 table "combined" 有一个字段名和一个外键字段 "helper"，它又是一个带有两个外键字段的 table。
我现在的问题是，什么是最简单的SQL-查询得到以下table：
[table workers]
ID [PK] | worker | combined-Name| department | location
--------+--------+--------------+------------+-----------
1 | John | name2 | Development| Paris
--------------------------------+------------+-----------
2 | Adam | name1 | Production | Berlin
我已经用一些 LEFT-JOINS 尝试过，但没能成功地将所有 "clearnames" 连接到 table "workers"
此查询有效：
SELECT w.ID, worker, c.name AS `combined-Name`, d.department, l.department as
location FROM workers w
LEFT JOIN combined c ON c.ID = w.combined
LEFT JOIN helper h ON h.ID = c.helper
LEFT JOIN departments d ON d.ID = h.department
LEFT JOIN location l ON l.ID = h.location
GROUP BY w.ID
我使用 AS 关键字将名称设置为您的首选输出。
这是使用提供的结构和数据在本地测试的。
它基本上是 4 个简单的左连接，然后 select 不是 select 外部表的名称列而是 ID 的 select。
引用c.name上的别名是因为我们需要转义特殊字符-
使用以下查询：
select [workers].worker,[combined].name as combined-name,[departments].name as department,[location].name as location from [workers]
left join [combined] on [workers].combined = [combined].combined
left join [helper] on [helper].ID = [combined].helper
left join [departments] on [departments].ID = [helper].department
left join [location] on [location].ID = [helper].location