查找在布鲁克林的所有分支机构拥有帐户的所有客户

Question

我有一些桌子：

“分支”表（分支名称、分支城市、资产）

“客户”表（客户名称、客户街道、客户城市）

“账户”表（account_number、branch_name、balance）

“贷款”表（loan_number、branch_name、amount）

“存款人”表（customer_name、account_number）

“借款人”表（customer_name、loan_number）

现在我想查找在布鲁克林的所有分行都有帐户的所有客户。这是我针对此问题的 SQL。但我想知道如何使用 TABLE JOIN，而不使用 EXCEPT 来解决这个问题。有人可以帮帮我吗?????谢谢。

SELECT distinct S.customer_name FROM depositor as S
WHERE not exists (
     (SELECT branch_name
      FROM branch
      WHERE branch_city = 'Brooklyn')
      EXCEPT
      (SELECT R.branch_name
       FROM depositor as T, account as R
       WHERE T.account_number = R.account_number and
             S.customer_name = T.customer_name ))

Answer 1

我想不出使用UNION 的方法。您的问题是找到在布鲁克林拥有所有分支机构的客户。基本上有两种方法可以解决这个问题。

解决方案 1 - 查找不不在布鲁克林拥有所有分支机构的客户。

（故意双重否定）。换句话说，找到所有在布鲁克林没有至少一家分店的客户，然后拿走其余的。

这就是您在示例中所做的。您将布鲁克林的所有分支机构 EXCEPT 客户拥有的分支机构，如果没有布鲁克林分支机构剩余，则客户拥有所有分支机构。您可以使用联接以另一种方式执行此操作，但您的可能更具可读性。

SELECT customer_name
FROM customer
WHERE customer_name NOT IN (
    SELECT d.customer_name
    FROM depositor d
    INNER JOIN branch brooklyn ON brooklyn.branch_city = 'Brooklyn'
    LEFT JOIN account a 
        ON d.account_number = a.account_number
        AND brooklyn.branch_name = a.branch_name 
    WHERE a.account_number IS NULL )

解决方案 2 - 查找在布鲁克林拥有与布鲁克林分支机构数量相同数量的所有客户。

为此，您需要使用GROUP BY 来获取每位客户的布鲁克林分支机构数量，然后您可以使用它与布鲁克林的分支机构总数进行比较。

SELECT d.customer_name
FROM depositor d
INNER JOIN account a ON d.account_number = a.account_number
INNER JOIN branch b ON a.branch_name = b.branch_name
WHERE b.branch_city = 'Brooklyn'
GROUP BY d.customer_name
HAVING COUNT(DISTINCT B.branch_name) = (
    SELECT COUNT(branch_name)
    FROM branch 
    WHERE branch_city = 'Brooklyn')

UNION 用于合并两个数据集。如果您的问题是......

“查找所有拥有布鲁克林分行账户或贷款的客户。”

...那么您可以使用UNION。

SELECT DISTINCT d.customer_name
FROM depositor d
INNER JOIN account a ON d.account_number = a.account_number
INNER JOIN branch b ON a.branch_name = b.branch_name
WHERE b.branch_city = 'Brooklyn'
UNION
SELECT DISTINCT l.customer_name
FROM borrower bo
INNER JOIN loan l ON bo.loan_number = l.loan_number
INNER JOIN branch b ON l.branch_name = b.branch_name
WHERE b.branch_city = 'Brooklyn'

Answer 2

Select A.customer_name
From depositor as A
Left join account as B
on B. account_number = A.account_number
group by A.customer_name
Having count(distinct(B.branch_name))  = 
(select count(branch_name) from branch where branch_city = 'Brooklyn')

Answer 3

假设您想要回答：“查找在布鲁克林的任何分行拥有帐户的所有客户”

select c.*
from customer c
inner join depositor d
   on c.customer_name = d.customer_name
inner join account a
   on d.account_numver = a.account_number
inner join branch b
   on a.branch_name = b.branch_name
where b.branch_city = 'Brooklyn'

如果一个客户可以拥有多个帐户，或者一个帐户可以拥有多个分支机构，则需要调整联接。