Question

我坚持以下问题。有两个表：

银行

bank_id [PK] | name
---------------------
 1            Bank_1
 2            Bank_2
 3            Bank_3
 4            Department_1
 5            Department_2
 6            Department_3

关系

id [PK] | parent_id | filial_id
--------------------------------   
 1         1            5
 2         2            4
 3         2            6

需要选择所有银行部门对。 还应选择没有部门的银行。

我写了以下查询：

SELECT A.name AS 'Bank', B.name  AS 'Department'
FROM banks A,
     banks B 
        JOIN relations ON B.bank_id=relations.filial_id
                      AND A.bank_id = relations.parent_id;

但它只显示有部门的银行。我应该如何将查询更改为输出字符串Bank_3，而该字符串没有部门？

Answer 1

我认为您的表格应如下所示

银行表格仅包含 bank_id，银行名称。 bank_id 将成为主键。
部门将有单独的表格，其中包括 bank_id，dept_id，dept_name
bank_id 将是来自银行表
部门ID 将成为部门表中的主键

您的银行表格将按以下方式划分。

    bank_id  bank_name
    1            Bank_1
    2            Bank_2
    3            Bank_3

    bank_id dept_id dept_name
       1     4            Department_1
       2     5            Department_2
       2     6            Department_3

然后，您只需使用左连接即可获得所需格式的数据。

目前，您的银行表中没有银行和部门的识别栏。

Answer 2

你可以用联盟

SELECT A.name AS 'Bank', B.name  AS 'Department' 
FROM  relations AS R 
INNER JOIN banks AS A ON A.bank_id = R.parent_id
INNER  JOIN banks AS B ON  B.bank_id=R.filial_id ;

UNION 

select name, null
from banks where bank_id not in (select parent_id from relation)

Answer 3

试试这个：

SELECT A.name AS 'Bank', B.name  AS 'Department' 
FROM (SELECT * FROM banks WHERE NOT EXISTS(SELECT TOP 1 1 FROM Relations WHERE filial_id = bank_id)) A
LEFT OUTER JOIN Relations r 
INNER JOIN banks B ON B.bank_id= r.filial_id ON   A.bank_id = r.parent_id

输出：

Bank                 Department
-------------------- --------------------
Bank_1               Department_2
Bank_2               Department_1
Bank_2               Department_3
Bank_3               NULL

Answer 4

部门都是relations.filial_id中存在的“银行”。银行都是没有的“银行”。使用外部联接来获取银行的部门，以便使银行没有部门。

select b.name as bank_name, d.name as department_name 
from (select * from banks where bank_id not in (select filial_id from relations) b
left join relations r on r.parent_id = b.bank_id
left join banks d on d.bank_id = r.filial_id

SQL Query自联接来自两个表

4 个答案: