如何为 SQL 中的每个日期返回一行？答案

【问题标题】：How to return a row for every date in SQL?如何为 SQL 中的每个日期返回一行？
【发布时间】：2023-01-29 20:28:50
【问题描述】：

我想从我的 MySQL 数据库中检索过去 7 天每个日期的交易总和，但有些日期没有任何交易。那些日子我如何返回 0？

这是我曾经处理过并尝试过的 SQL 查询，但是这个查询只提供那些在那些日子里确实有价值的查询。

SELECT COUNT(transaction_id) AS orders, SUM(amount) AS sales, CAST(time AS DATE) AS time FROM tbltransactions WHERE time BETWEEN CAST(? AS DATE) AND CAST(? AS DATE) GROUP BY CAST(time AS DATE) ORDER BY time ASC

【问题讨论】：

标签： mysql sql

【解决方案1】：

先尝试generate日期，然后加入你的数据表：

 SELECT COUNT(transaction_id) AS orders
      , SUM(amount) AS sales
      , CAST(dates.time AS DATE) AS time 
 FROM 
 (
    SELECT DATE_SUB(CURDATE(), INTERVAL 7 DAY) + INTERVAL num DAY AS time
    FROM 
    (
       SELECT 1 AS num UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7
     ) n 
  ) dates
 LEFT JOIN tbltransactions 
    ON dates.time = tbltransactions.time
 GROUP BY CAST(dates.time AS DATE) 
 ORDER BY dates.time ASC

这是测试数据：

CREATE TABLE tbltransactions (
  time DATE,
  transaction_id INT,
  amount DECIMAL(10,2)
);

INSERT INTO tbltransactions (time, transaction_id, amount)
VALUES 
  ('2023-01-20', 1, 100.00),
  ('2023-01-21', 2, 200.00),
  ('2023-01-27', 3, 300.00),
  ('2023-01-29', 4, 400.00),
  ('2023-01-29', 5, 500.00);

【讨论】：

【解决方案2】：

您可以使用带有 SELECT 语句的子查询来生成最近 7 天内所有日期的列表，然后将其与事务表进行 LEFT JOIN。这将为您提供一个没有交易的日期为 0 的结果集：

SELECT  dates.date, COALESCE(SUM(transactio s.amount), 0) AS total_amount FROM (SELECT DATE_SUB(CURDATE(),INTERVAL (7 + (@i := @i + 1)) DAY) AS date  FROM    (SELECT @i := -1) r, information_schema.tables  LIMIT 7) dates LEFT JOIN transactions ON dates.date =DATE(transactions.transaction_date) GROUP BY dates.date ORDER BY dates.date DESC;

【讨论】：