Mysql - 在記錄之前N天創建的最近記錄

我不知道這是否可能，但這裏是我正在尋找的Mysql - 在記錄之前N天創建的最近記錄

我需要當前日期，如果創建的最後一條記錄超過N天或創建的第一條記錄的created_at日期之後N天內創建的第一條記錄的created_at

因此，如果存在兩條記錄，其創建日期爲差異大於N天，並且在這兩個日期之間不會創建其他記錄，請爲我提供最近創建的這些記錄的created_at，除非最近的created_at中的所有記錄都大於N天前，在這種情況下，請提供今天的da TE代替

所以對於這個表和N = 5

+----+-------------+ 
|id |created_at | 
+----+-------------+ 
|9 |1 day ago | 
|8 |2 days ago | 
|7 |3 days ago | 
|6 |4 days ago | 
|5 |5 days ago | < not this date 
|4 |6 days ago | < get this date 
|3 |12 days ago | < not this date 
|2 |13 days ago | < not this date 
|1 |20 days ago | 
+----+-------------+

我需要得到6 days ago但不13 days ago或5 days ago，如果記錄看起來像這樣

+----+-------------+ 
|id |created_at | 
+----+-------------+ 
|5 |11 day ago | < not this date, instead today's date 
|4 |12 days ago | 
|3 |20 days ago | 
|2 |21 days ago | 
|1 |30 days ago | 
+----+-------------+

我需要今天的日期

來源

2016-11-21 Jarfis

是'created_at '約會或字面意思是「11天前」？ – WillardSolutions

這是一個日期，我只是覺得X天前更容易閱讀的例子 – Jarfis

如果日期是1,2,5,6,7,15天前，你想要15天前，因爲差距必須更大比N天多？ – Barmar

以查詢計算相鄰日期之間的差距開始：

SELECT created_at, DATEDIFF(@prevdate, created_at) AS diff, @prevdate := created_at 
FROM (SELECT created_at 
     FROM yourTable 
     WHERE created_at <= DATE_SUB(CURDATE(), INTERVAL @N DAY) 
     ORDER BY created_at DESC) AS x, 
CROSS JOIN (SELECT @prevdate := NULL) as vars

然後添加了行，其中diff超過N的過濾器，並選擇最近的這些

SELECT MAX(created_at) AS selected_date 
FROM (SELECT created_at, DATEDIFF(@prevdate, created_at) AS diff, @prevdate := created_at 
     FROM (SELECT created_at 
      FROM yourTable 
      WHERE created_at <= DATE_SUB(CURDATE(), INTERVAL @N DAY) 
      ORDER BY created_at DESC) AS x 
     CROSS JOIN (SELECT @prevdate := NULL) as vars) AS z 
WHERE diff > @N;

最後，爲了獲得當前的日期，如果最近的日期超過N天以前，您可以使用另一個查詢獲取最新日期，並使用IF()。

SELECT IF (latest_date < DATE_SUB(CURDATE(), INTERVAL @N DAY), CURDATE(), MAX(created_at)) AS selected_date 
FROM (SELECT created_at, DATEDIFF(@prevdate, created_at) AS diff, @prevdate := created_at 
    FROM (SELECT created_at 
      FROM yourTable 
      WHERE created_at <= DATE_SUB(CURDATE(), INTERVAL @N DAY) 
      ORDER BY created_at DESC) AS x 
    CROSS JOIN (SELECT @prevdate := NULL) as vars) AS z 
CROSS JOIN (SELECT MAX(created_at) AS latest_date FROM yourTable) AS y 
WHERE diff > @N;

DEMO

來源

2016-11-21 21:57:25 Barmar

我不認爲這是我正在尋找的，不會只是返回比N天之前的最新記錄更新的第一條記錄的created_at？ – Jarfis

這就是你要求的，但看起來你自從我發佈以來就改變了這個問題。 – Barmar

對不起，我在示例中的第一遍還不夠詳細 – Jarfis

我去

SELECT IF (latest_date < DATE_SUB(CURDATE(), INTERVAL @N DAY), CURDATE(), MAX(fetch_prevdate)) AS selected_date 
FROM (SELECT created_at, @prevdate as fetch_prevdate, DATEDIFF(@prevdate, created_at) AS diff, @prevdate := created_at 
     FROM (SELECT created_at 
      FROM yourTable 
      WHERE created_at <= DATE_SUB(CURDATE(), INTERVAL @N DAY) 
      ORDER BY created_at DESC) AS x 
     CROSS JOIN (SELECT @prevdate := NULL) as vars) AS z 
CROSS JOIN (SELECT MAX(created_at) AS latest_date FROM yourTable) AS y 
WHERE diff > @N;

Barmar的回答是一樣的，我需要什麼，但我有一個字段添加到的時間差子查詢之前存儲@prevdate值99％它被重新分配在select中並且得到MAX而不是created_at字段

來源

2016-11-22 19:21:58 Jarfis

Mysql - 在記錄之前N天創建的最近記錄

回答

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