如何根据其他记录的值更新字段

Question

我有一个类似于以下结构的 table：

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日期和结束日期的历史视图。一个城市的最新记录应该是开始日期最长的，结束日期为'0001-01-01 00:00:00'，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结束日期比下一个记录的开始日期早一秒，仅在 end_date 设置为“0001-01-01 00:00:00”。因此，在 end_date 有实际日期的情况下，该日期将被忽略。此外，最近 start_date 的城市记录不需要修改 end_date。

结果 table 应该如下所示：

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

我想过很多方法来以编程方式实现此目的，但是我喜欢一个通过 SQL 查询完全处理此问题的解决方案。我发现了一个类似的问题，答案是 here，但它不处理我的特殊情况。我怎样才能修改它以满足我的标准？

编辑：

我已根据以下陈述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_date 并不符合预期（例如 ID 号 5 和 6）。如下所示：

以下是能够复制的创建和插入语句：

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

您只需要 lead() 功能，MySQL 中没有。在 update 中使用变量具有挑战性，因此这里有一个具有相关子查询的方法。

获取下一个开始日期：

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;

您现在可以在 update 使用 join:

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

How to update fields based on value of other record

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