Question

我有一个银行数据库：

我想获取特定分支机构的客户名称和平均余额。也就是说，他们的储蓄帐户和支票帐户在“ x”分支的平均值。

我尝试了以下查询，但未成功。

我有这个查询：

SELECT DISTINCT customer_name, average_balance FROM 
(

  SELECT account_number, AVG(balance) AS average_balance
  FROM (
      SELECT account_number, balance FROM account WHERE account_number IN (SELECT account_number FROM savings_account)
  UNION ALL
  SELECT account_number, balance FROM account WHERE account_number IN (SELECT account_number FROM checking_account)
  ) AS subquery
  GROUP BY account_number
) AS subquery2 INNER JOIN customer;

示例输入语句：

INSERT INTO account VALUES ('ACC-101',  'Rock Ridge', 500000, '');
INSERT INTO account VALUES ('ACC-101',  'Beach Lookout',  1700, '');
INSERT INTO account VALUES ('ACC-102',  'Rock Ridge',  2465, '');
INSERT INTO account VALUES ('ACC-103',  'Rock Ridge',  77350, '');
INSERT INTO account VALUES ('ACC-104',  'Bargin Plaza', 480002, '');
INSERT INTO account VALUES ('ACC-105',  'Supreme Hill', 17000, '');
INSERT INTO account VALUES ('ACC-106',  'Rock Ridge',  5000, '');
INSERT INTO account VALUES ('ACC-107',  'Main Sperem',  3000, '');
INSERT INTO account VALUES ('ACC-108',  'Adus Avenue',  57685, '');


INSERT INTO savings_account VALUES('ACC-101', 0.1);
INSERT INTO savings_account VALUES('ACC-102', 0.7);
INSERT INTO savings_account VALUES('ACC-103',0.6);

INSERT INTO checking_account VALUES('ACC-104', 2000);
INSERT INTO checking_account VALUES('ACC-105', 2000);
INSERT INTO checking_account VALUES('ACC-106', 2000);

INSERT INTO depositor VALUES ('125-233-001',   'ACC-101',  '2012/10/13');
INSERT INTO depositor VALUES ('125-233-001',   'ACC-106',  '2013/09/21');
INSERT INTO depositor VALUES ('125-233-002',   'ACC-102',  '2014/08/11');
INSERT INTO depositor VALUES ('125-233-002',   'ACC-106',  '2015/07/06');
INSERT INTO depositor VALUES ('125-233-004',   'ACC-104',  '2016/06/11');
INSERT INTO depositor VALUES ('125-233-005',   'ACC-105',  '2012/05/17');
INSERT INTO depositor VALUES ('125-233-006',   'ACC-105',  '2018/10/11');
INSERT INTO depositor VALUES ('125-233-007',   'ACC-106',  '2019/02/27');
INSERT INTO depositor VALUES ('125-233-008',   'ACC-106',  '2012/01/31');

我得到下面的结果，但这不是我想要的

+--------------------+-----------------+
| customer_name      | average_balance |
+--------------------+-----------------+
| Chuck Delroy       |   500000.000000 |
| Chuck Delroy       |     2465.000000 |
| Chuck Delroy       |    77350.000000 |
| Chuck Delroy       |   480002.000000 |
| Chuck Delroy       |    17000.000000 |
| Chuck Delroy       |     5000.000000 |
| Dalrymple Fayval   |   500000.000000 |
| Dalrymple Fayval   |     2465.000000 |
| Dalrymple Fayval   |    77350.000000 |
| Dalrymple Fayval   |   480002.000000 |
| Dalrymple Fayval   |    17000.000000 |
| Dalrymple Fayval   |     5000.000000 |
| Freeman Mark       |   500000.000000 |
| Freeman Mark       |     2465.000000 |
| Freeman Mark       |    77350.000000 |
| Freeman Mark       |   480002.000000 |
| Freeman Mark       |    17000.000000 |
| Freeman Mark       |     5000.000000 |
| Trisman Kemar      |     2465.000000 |
| Trisman Kemar      |    77350.000000 |
| Trisman Kemar      |   480002.000000 |
| Trisman Kemar      |    17000.000000 |
| Trisman Kemar      |     5000.000000 |
+--------------------+-----------------+

示例：我实际上正在寻找的是

+--------------------+-----------------+
|Delroy Chuck        | 252,500.00.     |
+--------------------+-----------------+

这是因为他的储蓄帐户中有500,000，而支票帐户中有5000。

Answer 1

我看不到要加入客户的字段，因此我假设account和customer表中有一个字段customer_number。

首先，从您的原始查询中，

SELECT account_number, balance FROM account WHERE account_number IN (SELECT account_number FROM savings_account)

可以简化为

SELECT account_number, balance
FROM account
  INNER JOIN savings_account ON account.account_number = savings_account.account_number

我们要在这里包括客户以汇总平均值。

SELECT customer.customer_number, customer.customer_name, savings_account.account_number, savings_account.balance
FROM savings_account
  INNER JOIN account ON account.account_number = savings_account.account_number
  INNER JOIN customer ON account.customer_number = customer.customer_number

现在，对于下一步，我们将使用check_account进行合并。

SELECT customer.customer_number, customer.customer_name, checking_account.account_number, checking_account.balance
FROM checking_account
  INNER JOIN account ON account.account_number = checking_account.account_number
  INNER JOIN customer ON account.customer_number = customer.customer_number

然后可以将此查询与group by聚合。

之前：

SELECT customer_name, avg(balance)
FROM
(

    SELECT customer.customer_number, customer.customer_name, account.account_number, account.balance
    FROM  account
      INNER JOIN savings_account ON account.account_number = savings_account.account_number
      INNER JOIN customer ON account.customer_number = customer.customer_number

  UNION ALL
    SELECT customer.customer_number, customer.customer_name, account.account_number, account.balance
    FROM account
      INNER JOIN checking_account ON account.account_number = checking_account.account_number
      INNER JOIN customer ON account.customer_number = customer.customer_number
) AS subquery2
GROUP BY customer_number;

如何找到表中各列的平均值？

1 个答案: