mysql - 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 View 。城市的最新记录应该是开始日期最长的记录，结束日期为“0001-01-01 00:00:00”，表示尚无结束日期。

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下一条记录的开始日期前一秒，仅在 end_date 设置为“0001-”的情况下01-01 00:00:00'。因此，如果 end_date 具有实际日期，则该日期将被忽略。此外，具有最近的城市 start_date 的记录不需要修改 end_date。

生成的表格应如下所示:

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

我想过很多方法来以编程方式实现此目的，但是我希望有一个完全通过 SQL 查询来处理此问题的解决方案。我发现了一个类似的问题和答案 here ，但是它不能处理我的特定条件。我如何修改它以满足我的标准？

编辑:

根据此声明，我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，某些结束日期与预期不符(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()函数，该函数在MySQL中不可用。在 update 中使用变量具有挑战性，因此这里有一个带有相关子查询的方法。

要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;

您现在可以使用join在更新中使用它:

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;