MySQL5.6:寻求group_concat帮助

Question

我有桌子：

    CREATE TABLE IF NOT EXISTS `buildingAccess` (
    `id` int(10) unsigned NOT NULL,
      `building` varchar(16) NOT NULL,
      `person` varchar(16) NOT NULL,
      `enteryDate` datetime NOT NULL,
      `exitDate` datetime DEFAULT NULL
    ) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8;

    INSERT INTO `buildingAccess` (`id`, `building`, `person`, `enteryDate`, `exitDate`) VALUES
    (1, 'Lot B-3', 'Alice Jones', '2015-11-10 05:29:14', '2015-11-10 15:18:42'),
    (3, 'Lot B-3', 'Alice Jones', '2015-11-11 07:11:27', '2015-11-11 12:43:34'),
    (7, 'Lot B-3', 'Alice Jones', '2015-12-10 07:11:27', '2015-12-11 12:43:34'),
    (2, 'Lot B-3', 'Bill Mayhew', '2015-11-10 10:29:14', '2015-11-10 12:18:42'),
    (4, 'Lot B-3', 'Bill Mayhew', '2015-11-12 09:10:27', '2015-11-13 02:43:34'),
    (8, 'Lot B-3', 'Bill Mayhew', '2015-11-12 09:10:27', '2015-11-13 02:43:34'),
    (5, 'Lot B-3', 'Charlotte Ahn', '2015-12-01 05:29:14', NULL),
    (6, 'Lot B-3', 'Dennis Lowe', '2015-12-10 10:29:14', '2015-12-10 12:18:42');

    CREATE TABLE IF NOT EXISTS `buildingNotes` (
      `building` varchar(16) NOT NULL,
      `observer` varchar(16) NOT NULL,
      `observationDate` datetime NOT NULL,
      `note` varchar(64) NOT NULL
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

    INSERT INTO `buildingNotes` (`building`, `observer`, `observationDate`, `note`) VALUES
    ('Lot B-3', 'Alice Jones', '2015-11-10 05:32:12', 'burned out light on pole South-22'),
    ('Lot B-3', 'Alice Jones', '2015-11-10 05:39:12', 'burned out light on pole West-7'),
    ('Lot B-3', 'Alice Jones', '2015-11-10 05:42:12', 'overfull trash can near pole North-11'),
    ('Lot B-3', 'Charlotte Ahn', '2015-12-01 06:09:14', 'change drawr running low at gate 3');

    ALTER TABLE `buildingAccess`
     ADD PRIMARY KEY (`id`), ADD KEY `building` (`building`,`person`,`enteryDate`,`exitDate`);

    ALTER TABLE `buildingNotes`
     ADD KEY `building` (`building`,`observer`,`observationDate`,`note`);

    ALTER TABLE `buildingAccess`
    MODIFY `id` int(10) unsigned NOT NULL AUTO_INCREMENT,AUTO_INCREMENT=9;

我的目标是一个查询，返回buildingAccess表中所有记录的列表。每个字段都应该有一个notes字段，该字段是在该记录的日期/时间由buildingAccess.enteryDate和buildingAccess.exitDate括起来的所有buildingNotes.note条目的GROUP_CONCAT。

我试过几件事，但坚持住了：

    select 
        BA.building,
        BA.person,
        BA.enteryDate,
        IFNULL(BA.exitDate, NOW()),
        IFNULL(
            GROUP_CONCAT(
                '<p>',
                BN.observationDate, ': ',
                BN.observer, ': ', BN.note,
                '</p>'
                ORDER BY BN.observationDate ASC
                SEPARATOR ''
            ), 
            ''
        )
    from
        buildingAccess BA
        LEFT JOIN buildingNotes BN ON 
            BN.building = BA.building
            AND BN.observationDate BETWEEN BA.enteryDate AND BA.exitDate
    group by BN.building

这将返回：

+----------+---------------+---------------------+---------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| building | person        | enteryDate          | exitDate            | observations                                                                                                                                                                                                                     |
+----------+---------------+---------------------+---------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Lot B-3  | Charlotte Ahn | 2015-12-01 05:29:14 | 2016-01-23 23:04:04 |                                                                                                                                                                                                                                  |
| Lot B-3  | Alice Jones   | 2015-11-10 05:29:14 | 2015-11-10 15:18:42 | <p>2015-11-10 05:32:12: Alice Jones: burned out light on pole South-22</p><p>2015-11-10 05:39:12: Alice Jones: burned out light on pole West-7</p><p>2015-11-10 05:42:12: Alice Jones: overfull trash can near pole North-11</p> |
+----------+---------------+---------------------+---------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

我希望看到所有其他的buildingAccess记录，即使没有buildingNotes记录。

我假设我没有按正确的事物“分组”，但我还没有找到正确的组合。

指针？

Answer 1

我认为应该使用BN.building，它来自GROUP BY子句中的外部联接表。尝试以下几点：

SELECT
      BA.building
    , BA.person
    , BA.enteryDate
    , IFNULL(BA.exitDate, NOW())
    , IFNULL (
              GROUP_CONCAT (
                            '<p>',
                            BN.observationDate, ': ',
                            BN.observer, ': ', BN.note,
                            '</p>'
                            ORDER BY BN.observationDate ASC
                            SEPARATOR ''
                            )
                ,''
              )
FROM buildingAccess BA
      LEFT JOIN buildingNotes BN ON BN.building = BA.building
                  AND BN.observationDate BETWEEN BA.enteryDate AND BA.exitDate
GROUP BY
      BA.building
    , BA.person
    , BA.enteryDate
    , IFNULL(BA.exitDate, NOW())

这可能是太多行了，而且您可能需要一些其他方法来处理(例如)只获取日期而不是完整日期的时间。但是，您应该按caluse常规地指定组中查询的所有非聚合列。请参阅可拓MySQL群