Question

我一直在研究费用跟踪系统。我有三个主要表：'expenses'、'expense_reports'、'payments'。

我这样构建我的数据库：

'expenses' 属于一个 'expense_reports'
'expense_reports'有很多'费用'
'expense_reports' 属于许多'payments'
“payments”属于许多“expense_reports”

我为“expense_reports”和“payments”表添加了一个数据透视表，即“expense_report_payment”来处理多对多关系。 'expense_report_payment' 表有 ff 字段：

id
expense_report_id
payment_id
付款

这是我获取费用和付款总额的查询：

SELECT 
  IFNULL(SUM(ex.`amount`), 0) AS total_expenses,
  IFNULL(SUM(erp.`payment`), 0) AS total_payment 
FROM
  `expenses` ex 
  JOIN `expense_reports` er 
    ON er.`id` = ex.`expense_report_id` 
  LEFT JOIN `expense_report_payment` erp 
    ON erp.`expense_report_id` = er.`id` 
  JOIN `payments` p 
    ON p.`id` = erp.`payment_id` 
    AND p.`deleted_at` IS NULL 
    AND p.`cancelled_at` IS NULL 
    AND p.`received_at` IS NOT NULL 
WHERE ex.`deleted_at` IS NULL 
  AND er.`deleted_at` IS NULL 
  AND er.`rejected_at` IS NULL 
  AND er.`cancelled_at` IS NULL

如果收到付款，我会得到总金额（total_expenses = 100；total_payment = 100）。但是，如果尚未收到付款，则费用和付款的总金额为零。

Answer 1

LEFT JOIN 表。通常，您还应该将右联接表上的 WHERE 条件移动到 LEFT JOIN 的 ON 子句。试试

SELECT 
  IFNULL(SUM(ex.`amount`), 0) AS total_expenses,
  IFNULL(SUM(erp.`payment`), 0) AS total_payment 
FROM
  `expenses` ex 
  LEFT JOIN `expense_reports` er 
    ON er.`id` = ex.`expense_report_id` 
      AND er.`deleted_at` IS NULL 
      AND er.`rejected_at` IS NULL 
      AND er.`cancelled_at` IS NULL    
  LEFT JOIN `expense_report_payment` erp 
    ON erp.`expense_report_id` = er.`id` 
  LEFT JOIN `payments` p 
    ON p.`id` = erp.`payment_id` 
    AND p.`deleted_at` IS NULL 
    AND p.`cancelled_at` IS NULL 
    AND p.`received_at` IS NOT NULL 
WHERE ex.`deleted_at` IS NULL

Answer 2

谢谢大家的帮助。我设法通过在 LEFT JOIN 中加入 'expense_report_payment' 和 'payments' 表解决了这个问题。

SELECT 
  IFNULL(SUM(ex.`amount`), 0) AS total_expenses,
  IFNULL(SUM(erp.payment), 0) AS total_payment
FROM
  `expenses` ex 
  JOIN `expense_reports` er 
    ON er.`id` = ex.`expense_report_id` 
    AND er.`deleted_at` IS NULL 
    AND er.`rejected_at` IS NULL 
    AND er.`cancelled_at` IS NULL 
  LEFT JOIN 
    (SELECT 
      ep.*
    FROM
      `expense_report_payment` ep 
      JOIN `payments` p 
        ON p.`id` = ep.`payment_id`
    WHERE p.`received_at` IS NOT NULL
    AND p.`deleted_at` IS NULL
    AND p.`cancelled_at` IS NULL
    ) AS erp 
    ON erp.expense_report_id = er.`id` 
WHERE ex.`deleted_at` IS NULL

如何根据其他连接表条件选择某些表字段的总和？

2 个答案: