Question

我有一张类似于以下结构的表格：

City        start_date             end_date
Paris       1995-01-01 00:00:00    1997-10-01 23:59:59
Paris       1997-10-02 00:00:00    0001-01-01 00:00:00
Paris       2013-01-25 00:00:00    0001-01-01 00:00:00
Paris       2015-04-25 00:00:00    0001-01-01 00:00:00
Berlin      2014-11-01 00:00:00    0001-01-01 00:00:00
Berlin      2014-06-01 00:00:00    0001-01-01 00:00:00
Berlin      2015-09-11 00:00:00    0001-01-01 00:00:00
Berlin      2015-10-01 00:00:00    0001-01-01 00:00:00
Milan       2001-01-01 00:00:00    0001-01-01 00:00:00
Milan       2005-10-02 00:00:00    2006-10-02 23:59:59
Milan       2006-10-03 00:00:00    2015-04-24 23:59:59
Milan       2015-04-25 00:00:00    0001-01-01 00:00:00

数据包含基于城市的开始和结束日期的历史视图。城市的最新记录应该是具有最高开始日期和结束日期为＆＃0001; 0001-01-01 00：00：00＆＃39;，表示还没有结束日期。

我需要清理这些数据并确保每个城市的历史记录都有在下一个记录的开始日期前一秒，仅在设置了end_date的情况下到＃0001; 0001-01-01 00：00：00＆＃39;。因此，在end_date具有实际日期的情况下，将忽略该日期。此外，具有最近一个城市的start_date的记录不需要修改end_date。

结果表应如下所示：

City        start_date             end_date
Paris       1995-01-01 00:00:00    1997-10-01 23:59:59
Paris       1997-10-02 00:00:00    2013-01-24 23:59:59
Paris       2013-01-25 00:00:00    2015-04-24 23:59:59
Paris       2015-04-25 00:00:00    0001-01-01 00:00:00
Berlin      2014-11-01 00:00:00    2014-05-31 23:59:59
Berlin      2014-06-01 00:00:00    2015-09-10 23:59:59
Berlin      2015-09-11 00:00:00    2015-09-30 23:59:59
Berlin      2015-10-01 00:00:00    0001-01-01 23:59:59
Milan       2001-01-01 00:00:00    2005-10-01 23:59:59
Milan       2005-10-02 00:00:00    2006-10-02 23:59:59
Milan       2006-10-03 00:00:00    2015-04-24 23:59:59
Milan       2015-04-25 00:00:00    0001-01-01 00:00:00

我已经想到了很多以编程方式实现此目的的方法，但我希望能够通过SQL查询完全处理这个问题的解决方案。我找到了一个回答here的类似问题，但是它没有处理我的特定条件。如何修改它以满足我的标准？

修改

我根据以下声明尝试了以下建议的答案：

update test join
       (select t.*,
               (select min(start_date)
                from test t2
                where t2.city = t.city and
                      t2.start_date > t.start_date
                order by t2.start_date
                limit 1
               ) as next_start_date
        from test t
       ) tt
       on tt.city = test.city and tt.start_date = test.start_date
    set test.end_date = date_sub(tt.next_start_date, interval 1 second)
where test.end_date = '0001-01-01' and
      next_start_date is not null;

不幸的是，从柏林记录开始，有些end_dates不符合预期（例如id号为5和6）。如下所示：

以下是能够复制的create和insert语句：

CREATE TABLE `test` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `city` varchar(50) DEFAULT NULL,
  `start_date` datetime DEFAULT NULL,
  `end_date` datetime DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=13 DEFAULT CHARSET=utf8;

INSERT INTO test (city, start_date, end_date) VALUES ('Paris','1995-01-01 00:00:00','1997-10-01 23:59:59');
INSERT INTO test (city, start_date, end_date) VALUES ('Paris','1997-10-02 00:00:00','0001-01-01 00:00:00');
INSERT INTO test (city, start_date, end_date) VALUES ('Paris','2013-01-25 00:00:00','0001-01-01 00:00:00');
INSERT INTO test (city, start_date, end_date) VALUES ('Paris','2015-04-25 00:00:00','0001-01-01 00:00:00');
INSERT INTO test (city, start_date, end_date) VALUES ('Berlin','2014-11-01 00:00:00','0001-01-01 00:00:00');
INSERT INTO test (city, start_date, end_date) VALUES ('Berlin','2014-06-01 00:00:00','0001-01-01 00:00:00');
INSERT INTO test (city, start_date, end_date) VALUES ('Berlin','2015-09-11 00:00:00','0001-01-01 00:00:00');
INSERT INTO test (city, start_date, end_date) VALUES ('Berlin','2015-10-01 00:00:00','0001-01-01 00:00:00');
INSERT INTO test (city, start_date, end_date) VALUES ('Milan','2001-01-01 00:00:00','0001-01-01 00:00:00');
INSERT INTO test (city, start_date, end_date) VALUES ('Milan','2005-10-02 00:00:00','2006-10-02 23:59:59');
INSERT INTO test (city, start_date, end_date) VALUES ('Milan','2006-10-03 00:00:00','2015-04-24 23:59:59');
INSERT INTO test (city, start_date, end_date) VALUES ('Milan','2015-04-25 00:00:00','0001-01-01 00:00:00');

Answer 1

你需要lead()函数，这在MySQL中是不可用的。在update中使用变量具有挑战性，因此这是一个带有相关子查询的方法。

要获得下一个开始日期：

select t.*,
       (select min(start_date)
        from t t2
        where t2.city = t.city and
              t2.start_date > t.start_date
        order by t2.start_date
        limit 1
       ) as next_start_date
from t;

现在，您可以使用update：

在join中使用此功能

update t join
       (select t.*,
               (select min(start_date)
                from t t2
                where t2.city = t.city and
                      t2.start_date > t.start_date
                order by t2.start_date
                limit 1
               ) as next_start_date
        from t
       ) tt
       on tt.city = t.city and tt.start_date = t.start_date
    set t.end_date = date_sub(tt.next_start_date, interval 1 second)
where t.end_date = '0001-01-01' and
      t.next_start_date is not null;

如何根据其他记录的值更新字段

1 个答案: