获取字段第一次更改为当前值的日期。

Question

这是一件相当尴尬的事情，用语言表达，但我希望当项目第一次转到一个关税/客户时行。如果一个项目切换了客户，那么无论关税的差异如何，都应该返回切换的日期。如果项目切换项目，则返回的日期不得更改，除非新项目的收费与旧项目不同。

我不太清楚怎样才能说得更清楚，但我愿意听取建议。

我的查询如下：

SET @id = 1;
SELECT DISTINCT
    ip.ItemID,
    ip.ProjectID,
    p.TariffID,
    p.CustomerID,
    cs.Date
FROM item_project ip
LEFT JOIN item_project ip1
    ON ip.ItemID = ip1.ItemID
    AND ip.Date < ip1.Date
LEFT JOIN project p
    ON ip.ProjectID = p.ProjectID
LEFT JOIN (
    SELECT
        ip.ItemID,
        ip.Date
    FROM item_project ip
    LEFT JOIN item_project ip1
        ON ip.ProjectID = ip1.ProjectID
        AND ip.Date > ip1.Date
    LEFT JOIN project p
        ON ip.ProjectID = p.ProjectID
    WHERE ip.ItemID = @id
        AND ip1.ItemID IS NULL
        AND p.CustomerID = (
            SELECT p.CustomerID
            FROM project p
            LEFT JOIN item_project ip
                ON p.ProjectID = ip.ProjectID
            LEFT JOIN item_project ip1
                ON ip.ItemID = ip1.ItemID
                AND ip.Date < ip1.Date
            WHERE ip.ItemID = @id
                AND ip1.ItemID IS NULL
            )
        AND p.TariffID = (
            SELECT p.TariffID
            FROM project p
            LEFT JOIN item_project ip
                ON p.ProjectID = ip.ProjectID
            LEFT JOIN item_project ip1
                ON ip.ItemID = ip1.ItemID
                AND ip.Date < ip1.Date
            WHERE ip.ItemID = @id
                AND ip1.ItemID IS NULL
            )
) AS cs
    ON ip.ItemID = cs.ItemID
WHERE ip.ItemID = @id
    AND ip1.ItemID IS NULL

这给了我

"ItemID","ProjectID","TariffID","CustomerID","Date"
"1","2","1","1","2010-11-10 00:00:00"

哪一个日期不对？

SET @id=2给了我：

"2","2","1","1",NULL

这是正确的，除了日期

SET @id=3给了我：

"3","2","1","1",NULL

这也是正确的，除了日期。

这是数据库

CREATE TABLE IF NOT EXISTS `item_project` (
  `ID` int(10) unsigned NOT NULL auto_increment,
  `ItemID` varchar(10) NOT NULL,
  `ProjectID` int(10) unsigned NOT NULL,
  `Date` timestamp NOT NULL default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP,
  PRIMARY KEY  (`ID`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=latin1;

INSERT INTO `item_project` (`ID`, `ItemID`, `ProjectID`, `Date`) VALUES
    (1, '1', 1, '2010-11-05 00:00:00'),
    (2, '1', 2, '2010-11-10 00:00:00'),
    (3, '1', 3, '2010-11-20 00:00:00'),
    (4, '2', 2, '2010-11-21 00:00:00'),
    (5, '3', 4, '2010-11-21 00:00:00'),
    (6, '3', 2, '2010-11-22 00:00:00'),
    (7, '1', 2, '2010-11-23 00:00:00'),

CREATE TABLE IF NOT EXISTS `project` (
  `ProjectID` int(10) unsigned NOT NULL auto_increment,
  `Name` varchar(45) NOT NULL,
  `TariffID` varchar(45) NOT NULL,
  `CustomerID` varchar(45) NOT NULL,
  PRIMARY KEY  (`ProjectID`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=latin1;

INSERT INTO `project` (`ProjectID`, `Name`, `TariffID`, `CustomerID`) VALUES
    (1, 'Test', '2', '1'),
    (2, 'Another test', '1', '1'),
    (3, 'Project1', '1', '1'),
    (4, 'Main project', '2', '2');

CREATE TABLE IF NOT EXISTS `tariff` (
  `TariffID` int(10) unsigned NOT NULL auto_increment,
  `Tariff` varchar(45) NOT NULL,
  PRIMARY KEY  (`TariffID`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=latin1;

INSERT INTO `tariff` (`TariffID`, `Tariff`) VALUES
    (1, 'Tariff 1'),
    (2, 'Tariff 2');

编辑：一个项目可以追溯到旧的关税或客户。在这种情况下，显示的日期应该是发生这种情况的日期。

Answer 1

有趣的情况。这是我想出来的

SELECT i_general.ItemID, ProjectID, TariffID, CustomerID, the_date
FROM
(
    SELECT 
        ip.ItemID,
        p.ProjectID,
        p.TariffID,
        p.CustomerID
    FROM item_project ip
    INNER JOIN project p ON ip.ProjectID = p.ProjectID
    INNER JOIN tariff t ON p.TariffID = t.TariffID
    INNER JOIN (
        SELECT 
            ip.ItemID, MAX(Date) AS max_date
        FROM item_project ip
        GROUP BY ip.ItemID
        ) ip_max ON ip_max.ItemID=ip.ItemID AND ip_max.max_date=ip.Date
) i_general
INNER JOIN (
    SELECT ip1.ItemID, IF(MIN(ip2.Date) IS NULL,MIN(ip1.Date),MIN(ip2.Date)) AS the_date  
    FROM item_project ip1
    INNER JOIN project p1 ON ip1.ProjectID = p1.ProjectID
    LEFT JOIN item_project ip2 ON ip1.ItemID=ip2.ItemID AND ip1.Date < ip2.Date  
    LEFT JOIN project p2 ON ip2.ProjectID = p2.ProjectID AND (p2.TariffID!=p1.TariffID OR p2.CustomerID!=p1.CustomerID)
    GROUP BY ip1.ItemID
    ) i_date_info ON i_date_info.ItemID = i_general.ItemID

当然，您可以在您认为合适的情况下插入一些WHERE ItemID = @id。内部查询越多，越好。

无论如何，它都会导致

+--------+-----------+----------+------------+---------------------+
| ItemID | ProjectID | TariffID | CustomerID | the_date            |
+--------+-----------+----------+------------+---------------------+
| 1      |         3 | 1        | 1          | 2010-11-10 00:00:00 |
| 2      |         2 | 1        | 1          | 2010-11-21 00:00:00 |
| 3      |         2 | 1        | 1          | 2010-11-22 00:00:00 |
+--------+-----------+----------+------------+---------------------+

因此，它似乎可以使用现有的数据集。让我知道，如果你能提供的测试数据，但它是无效的。