Question

我一直在讨论如何在MySQL的限制内编写特定视图。

以下表格和列非常重要：

CREATE TABLE `invoices` (
  `id` int(10) unsigned NOT NULL AUTO INCREMENT,
  PRIMARY KEY (`id`)
)

-- Joins payments to invoices. The sum of all `invoice_currency_value`s is the balance paid towards an invoice.
CREATE TABLE `financial_transactions_invoices` (
  `id` int(10) unsigned NOT NULL AUTO INCREMENT,
  `invoice` int(10) unsigned NOT NULL,
  `invoice_currency_value` decimal(8,2) unsigned NOT NULL,
  PRIMARY KEY (`id`)
)

-- Lists items (services) available to purchase.
CREATE TABLE `items` (
  `id` int(10) unsigned NOT NULL AUTO INCREMENT,
  `value` decimal(8,2) unsigned NOT NULL
  PRIMARY KEY (`id`)
)

-- Each instance represents that the `item` has been purchased.
CREATE TABLE `item_instances` (
  `id` int(10) unsigned NOT NULL AUTO INCREMENT,
  `invoice` int(10) unsigned NOT NULL,
  `item` int(10) unsigned NOT NULL,
  `invoice_currency_rate` decimal(11,5) unsigned NOT NULL,
  PRIMARY KEY (`id`)
)

-- Any number of tax instances can exist for an item instance and indicate this tax has been applied to the associated item instance.
CREATE TABLE `tax_instances` (
  `id` int(10) unsigned NOT NULL AUTO INCREMENT,
  `item_instance` int(10) unsigned NOT NULL,
  `value` decimal(8,2) unsigned NOT NULL,
  PRIMARY KEY (`id`)
)

现在，我需要一个列出每行的视图

发票号
发票的总价值
发票上的总税金
以及对发票付款的总价值

但是，我无法弄清楚如何将这三个单独的查询分成每个发票一行的相同结果集，例如

inv_no  total_value     total_tax       payments
1       150             5               120
2       120             10              20
3       10              0               10
4       1000            150             1150

我编写了以下查询来生成所需的结果，但由于MySQL视图中的“无子查询”规则，这是不可接受的。

SELECT `invoice_id`, SUM(`total_value`) AS `total_value`, SUM(`total_tax`) AS `total_tax`,
    SUM(`paid_balance`) AS `paid_balance`
FROM
(SELECT `invoices`.`id` AS `invoice_id`, SUM(`items`.`value` * `item_instances`.`invoice_currency_rate`) AS `total_value`,
    NULL AS `total_tax`, NULL AS `paid_balance`
FROM `items`
    JOIN `item_instances` ON `items`.`id` = `item_instances`.`item`
    JOIN `invoices` ON `item_instances`.`invoice` = `invoices`.`id`
GROUP BY `invoices`.`id`
UNION
SELECT `invoices`.`id`, NULL, SUM(`tax_instances`.`value`), NULL
FROM `tax_instances`
    JOIN `item_instances` ON `tax_instances`.`item_instance` = `item_instances`.`id`
    JOIN `invoices` ON `item_instances`.`invoice` = `invoices`.`id`
GROUP BY `invoices`.`id`
UNION
SELECT `invoices`.`id`, NULL, NULL, SUM(`financial_transactions_invoices`.`invoice_currency_value`)
FROM `financial_transactions_invoices`
    JOIN `invoices` ON `financial_transactions_invoices`.`invoice` = `invoices`.`id`
GROUP BY `invoices`.`id`) AS `components`
GROUP by `invoice_id`;

如果不以我的方式解决问题，我想不出任何其他方式我可以在MySQL中。

有什么想法吗？感谢任何帮助。

Answer 1

您可以创建两个视图。一个包含UNION子查询，另一个包含外部查询。

SQL将结果集中的列'合并'到一个结果集中

1 个答案: