用于识别表中序列的 ​​MySql 查询

Question

我需要有关 mysql 查询的帮助，以根据一系列进入和退出日期更新同一表的新列。

下表:

╔════╦═══════════╦═════════════╦═════════════╦════════════════════╗
║ ID ║   PLACE   ║  ENTRYDATE  ║  EXITDATE   ║ LAST_PLACE_VISITED ║
╠════╬═══════════╬═════════════╬═════════════╬════════════════════╣
║  1 ║ Delhi     ║ 1-Jan-2012  ║ 5-Jan-2012  ║                    ║
║  1 ║ Agra      ║ 10-Jan-2012 ║ 11-Jan-2012 ║                    ║
║  1 ║ Bangalore ║ 21-Jan-2012 ║ 24-Jan-2012 ║                    ║
║  1 ║ Mumbai    ║ 12-Jan-2012 ║ 19-Jan-2012 ║                    ║
║  2 ║ LA        ║ 1-Mar-2012  ║ 3-Mar-2012  ║                    ║
║  2 ║ SFO       ║ 10-Mar-2012 ║ 14-Mar-2012 ║                    ║
║  2 ║ NY        ║ 4-Mar-2012  ║ 9-Mar-2012  ║                    ║
║  3 ║ Delhi     ║ 12-Apr-2012 ║ 13-Apr-2012 ║                    ║
╚════╩═══════════╩═════════════╩═════════════╩════════════════════╝

ENTRYDATE 和 EXITDATE 的数据类型是DATE。

根据上表，我需要编写一个查询以根据 ID 的进入和退出日期更新“Last_Place_Visited”列。

如果您对此查询有任何帮助，我们将不胜感激。

谢谢。巴尔加夫

Answer 1

因为 MySQL 不支持窗口函数，所以这是一个非常困惑的问题，

UPDATE  TravelTbl a
        INNER JOIN
        (
            SELECT  a.ID, 
                    a.Place, 
                    a.EntryDate, 
                    a.ExitDate, 
                    b.Place Last_Place_Visited
            FROM
                    (
                        SELECT  ID,
                                Place,
                                EntryDate,
                                ExitDate,
                                Last_Place_Visited,
                                @grp := if(@ID = ID, @grp ,0) + 1 GRP_RecNo,
                                @ID := ID
                        FROM    TravelTbl,
                                (SELECT @ID := '', @grp := 0) vars
                        ORDER   BY  EntryDate
                    ) a
                    LEFT JOIN
                    (
                        SELECT  ID,
                                Place,
                                EntryDate,
                                ExitDate,
                                Last_Place_Visited,
                                @grp2 := if(@ID2 = ID, @grp2 ,0) + 1 GRP_RecNo,
                                @ID2 := ID
                        FROM    TravelTbl,
                                (SELECT @ID2 := '', @grp2 := 0) vars
                        ORDER   BY  EntryDate
                    ) b ON  a.ID = b.ID AND
                            a.GRP_RecNo = b.GRP_RecNo + 1
        ) b ON  a.ID = b.ID AND
                a.Place = b.Place AND
                a.EntryDate = b.EntryDate AND
                a.ExitDate = b.ExitDate AND
                b.Last_Place_Visited IS NOT NULL
SET     a.Last_Place_Visited = b.Last_Place_Visited

• SQLFiddle Demo

输出

╔════╦═══════════╦═════════════╦═════════════╦════════════════════╗
║ ID ║   PLACE   ║  ENTRYDATE  ║  EXITDATE   ║ LAST_PLACE_VISITED ║
╠════╬═══════════╬═════════════╬═════════════╬════════════════════╣
║  1 ║ Delhi     ║ 1-Jan-2012  ║ 5-Jan-2012  ║ (null)             ║
║  1 ║ Agra      ║ 10-Jan-2012 ║ 11-Jan-2012 ║ Delhi              ║
║  1 ║ Bangalore ║ 21-Jan-2012 ║ 24-Jan-2012 ║ Mumbai             ║
║  1 ║ Mumbai    ║ 12-Jan-2012 ║ 19-Jan-2012 ║ Agra               ║
║  2 ║ LA        ║ 1-Mar-2012  ║ 3-Mar-2012  ║ (null)             ║
║  2 ║ SFO       ║ 10-Mar-2012 ║ 14-Mar-2012 ║ NY                 ║
║  2 ║ NY        ║ 4-Mar-2012  ║ 9-Mar-2012  ║ LA                 ║
║  3 ║ Delhi     ║ 12-Apr-2012 ║ 13-Apr-2012 ║ (null)             ║
╚════╩═══════════╩═════════════╩═════════════╩════════════════════╝