【问题标题】：Using MySQL GROUP_CONCAT or PIVOT on multiple joined tables在多个连接表上使用 MySQL GROUP_CONCAT 或 PIVOT
【发布时间】：2012-09-10 10:03:49
【问题描述】：

问题

我正在为一所学校开发内容管理系统，我希望能够创建多个连接表的视图。除了加入表之外，我还需要执行 PIVOT 或 GROUP_CONCAT（或其他一些函数）以便从每个表中获取多行并将它们用作视图中的列。为了帮助可视化，这里是我正在使用的简化：

设置

结构：

DROP TABLE IF EXISTS `date`;
CREATE TABLE `date` (
  `col_pkid` int(11) NOT NULL AUTO_INCREMENT,
  `col_guid` varchar(100) NOT NULL DEFAULT '',
  `col_entry` varchar(100) NOT NULL,
  `col_inquiry_name` varchar(100) NOT NULL,
  `col_value` int(11) DEFAULT NULL,
  PRIMARY KEY (`col_pkid`)
);

DROP TABLE IF EXISTS `bigText`;
CREATE TABLE `bigText` (
  `col_pkid` int(11) NOT NULL AUTO_INCREMENT,
  `col_guid` varchar(100) NOT NULL DEFAULT '',
  `col_entry` varchar(100) NOT NULL,
  `col_inquiry_name` varchar(100) NOT NULL,
  `col_value` text,
  PRIMARY KEY (`col_pkid`)
);

DROP TABLE IF EXISTS `smallText`;
CREATE TABLE `smallText` (
  `col_pkid` int(11) NOT NULL AUTO_INCREMENT,
  `col_guid` varchar(100) NOT NULL,
  `col_entry` varchar(100) NOT NULL,
  `col_inquiry_name` varchar(100) NOT NULL,
  `col_value` varchar(100) DEFAULT '',
  PRIMARY KEY (`col_pkid`)
);

数据：

INSERT INTO `date` (`col_pkid`, `col_guid`, `col_entry`, `col_inquiry_name`, `col_value`)
VALUES
    (1,'d2kih1ho5z','1','Semester',1294834220),
    (2,'d2kih1j99y','2','Semester',1327077210);

INSERT INTO `bigText` (`col_pkid`, `col_guid`, `col_entry`, `col_inquiry_name`, `col_value`)
VALUES
    (16,'d2kih1kxwh','1','Description','Lorem ipsum dolor sit amet...'),
    (17,'d2kih1mhnn','2','Description','Consectetur adipiscing elit...');

INSERT INTO `smallText` (`col_pkid`, `col_guid`, `col_entry`, `col_inquiry_name`, `col_value`)
VALUES
    (1,'d2kih1njuj','1','Title','Addition and Subtraction'),
    (2,'d2kih1ot0x','1','Course','Math'),
    (16,'d2kj5osy71','1','Location','Building 7'),
    (17,'d2kj5p0z8f','1','Teachers','John'),
    (18,'d2kj5p5efi','1','Teachers','Jane'),
    (19,'d2kj5p98xv','1','Teachers',''),
    (20,'d2kj5pasi9','1','Teachers',''),
    (21,'d2kj5pbqbg','1','Teachers',''),
    (22,'d2kj5pdxdb','2','Title','Reading Mark Twain'),
    (23,'d2kih198do','2','Course','Literature'),
    (24,'d2kj5opcgo','2','Location','Building 4'),
    (25,'d2hd00n5eb','2','Teachers','Billy'),
    (26,'d2hea3jo74','2','Teachers','Bob'),
    (27,'d2hec78m5e','2','Teachers',''),
    (28,'d2hec7bnar','2','Teachers',''),
    (29,'d2hec7cbrq','2','Teachers','');

一些失败的尝试

通过执行以下操作，我可以将表格很好地连接在一起：

DROP VIEW IF EXISTS entries;
CREATE VIEW entries AS
SELECT
    st.col_entry,
    if(st.col_inquiry_name = 'Title', st.col_value, NULL) AS 'Title', 
    if(st.col_inquiry_name = 'Course', st.col_value, NULL) AS 'Course',
    if(bt.col_inquiry_name = 'Description', bt.col_value, NULL) AS 'Description',
    if(d.col_inquiry_name = 'Semester', d.col_value, NULL) AS 'Semester',
    if(st.col_inquiry_name = 'Location', st.col_value, NULL) AS 'Location',
    if(st.col_inquiry_name = 'Teachers', st.col_value, NULL) AS 'Teachers'
FROM smallText st
INNER JOIN bigText bt
ON st.col_entry = bt.col_entry
INNER JOIN date d
ON bt.col_entry = d.col_entry
GROUP BY col_entry;

但在这里我只从每个表中获取第一行的值。这就是我尝试介绍GROUP_CONCAT 的原因，尽管我在这方面也没有取得太大的成功：

DROP VIEW IF EXISTS entries;
CREATE VIEW entries AS
SELECT
    st.col_entry,
    GROUP_CONCAT(if(st.col_inquiry_name = 'Title', st.col_value, NULL)) AS 'Title', 
    GROUP_CONCAT(if(st.col_inquiry_name = 'Course', st.col_value, NULL)) AS 'Course',
    GROUP_CONCAT(if(bt.col_inquiry_name = 'Description', bt.col_value, NULL)) AS 'Description',
    GROUP_CONCAT(if(d.col_inquiry_name = 'Semester', d.col_value, NULL)) AS 'Semester',
    GROUP_CONCAT(if(st.col_inquiry_name = 'Location', st.col_value, NULL)) AS 'Location',
    GROUP_CONCAT(if(st.col_inquiry_name = 'Teachers', st.col_value, NULL)) AS 'Teachers'
FROM smallText st
INNER JOIN bigText bt
ON st.col_entry = bt.col_entry
INNER JOIN date d
ON bt.col_entry = d.col_entry
GROUP BY col_entry;

我能够让视图中的每一列都填充了表中的相应值，但是 date 和 bigText 列根据它们加入的原始行数（7 次）被复制。

（另外，作为另一个复杂级别...我希望拥有它，以便不同的老师也能找到自己的列：Teacher_01、Teacher_02、..Teacher_05，我会猜想这可能涉及对我所拥有的东西进行重大重组。）

谢谢！

...更新

因此，我能够生成一个查询，该查询输出的内容与我正在寻找的内容更接近，但我无法在视图中使用它，因为FROM 子句中有一个子查询：

SELECT
st.col_entry,
Title,
Course,
Description,
Semester,
Location,
Teachers
FROM smallText st
JOIN (SELECT smallText.col_entry, GROUP_CONCAT(if(smallText.col_inquiry_name = 'Title', smallText.col_value, NULL)) AS 'Title' 
    FROM smallText GROUP BY smallText.col_entry) a
ON a.col_entry = st.col_entry
JOIN (SELECT smallText.col_entry, GROUP_CONCAT(if(smallText.col_inquiry_name = 'Course', smallText.col_value, NULL)) AS 'Course'
    FROM smallText GROUP BY smallText.col_entry) b
ON b.col_entry = st.col_entry
JOIN (SELECT bigText.col_entry, GROUP_CONCAT(if(bigText.col_inquiry_name = 'Description', bigText.col_value, NULL)) AS 'Description'
    FROM bigText GROUP BY bigText.col_entry) c
ON c.col_entry = st.col_entry
JOIN (SELECT date.col_entry, GROUP_CONCAT(if(date.col_inquiry_name = 'Semester', date.col_value, NULL)) AS 'Semester'
    FROM date GROUP BY date.col_entry) d
ON d.col_entry = st.col_entry
JOIN (SELECT smallText.col_entry, GROUP_CONCAT(if(smallText.col_inquiry_name = 'Location', smallText.col_value, NULL)) AS 'Location'
    FROM smallText GROUP BY smallText.col_entry) e
ON e.col_entry = st.col_entry
JOIN (SELECT smallText.col_entry, GROUP_CONCAT(if(smallText.col_inquiry_name = 'Teachers', smallText.col_value, NULL)) AS 'Teachers'
    FROM smallText GROUP BY smallText.col_entry) f
ON f.col_entry = st.col_entry
GROUP BY st.col_entry

结果

此查询的输出如下所示：

Entry   Title                           Course      Description                     Semester    Location    Teachers
---------------------------------------------------------------------------------------------------------------------------------
1       Addition and Subtraction        Math        Lorem ipsum dolor sit amet...   1294834220  Building 7  NULL
2       Reading Mark Twain              Literature  Consectetur adipiscing elit...  1327077210  Building 4  NULL

除了空的Teachers 列之外，这基本上是我正在寻找的（但以某种方式生成，我可以在视图中使用查询）。

此外，正如我上面提到的，我希望能够将同一 inquiry_name 的多个值提取到单独的列中。所以最终所需的输出如下所示：

期望的结果

Entry   Title                           Course      Description                     Semester    Location    Teachers_01 Teachers_02 Teachers_03 Teachers_04 Teachers_05
---------------------------------------------------------------------------------------------------------------------------------
1       Addition and Subtraction        Math        Lorem ipsum dolor sit amet...   1294834220  Building 7  John        Jane        NULL        NULL        NULL
2       Reading Mark Twain              Literature  Consectetur adipiscing elit...  1327077210  Building 4  Billy       Bob         NULL        NULL        NULL

谢谢！

【问题讨论】：

很棒的职位发布示例数据和表结构（以及您尝试过的内容），但是您能否提供所需结果的示例？
更新了帖子。感谢您的提示。

标签： mysql sql pivot group-concat

【解决方案1】：

这是一个模拟-PIVOT 将rownum 应用于教师：

select s.col_entry,
  max(case when s.col_inquiry_name = 'Title' then s.col_value end) AS 'Title',
  max(case when s.col_inquiry_name = 'Course' then s.col_value end) AS 'Course',
  max(case when b.col_inquiry_name = 'Description' then b.col_value end) AS 'Description',
  max(case when d.col_inquiry_name = 'Semester' then d.col_value end) AS 'Semester',
  max(case when s.col_inquiry_name = 'Location' then s.col_value end) AS 'Location',
  max(case when tch.grp = 'Teachers_01' then tch.col_value end) AS 'Teachers_01',
  max(case when tch.grp = 'Teachers_02' then tch.col_value end) AS 'Teachers_02',
  max(case when tch.grp = 'Teachers_03' then tch.col_value end) AS 'Teachers_03',
  max(case when tch.grp = 'Teachers_04' then tch.col_value end) AS 'Teachers_04',
  max(case when tch.grp = 'Teachers_05' then tch.col_value end) AS 'Teachers_05'
from smallText s
left join bigText b
  on s.col_entry = b.col_entry 
left join date d
  on b.col_entry = d.col_entry 
left join
(
  select col_entry, col_value, concat('Teachers_0', group_row_number) grp
  from
  (
    select col_entry, col_value,
      @num := if(@col_entry = `col_entry`, @num + 1, 1) as group_row_number,
      @col_entry := `col_entry` as dummy
    from smallText , (SELECT @rn:=0) r
    where col_inquiry_name = 'Teachers'
      and col_value != ''
  ) x
) tch
  on s.col_entry = tch.col_entry
group by s.col_entry;

见SQL Fiddle with demo

编辑#1，根据您提供的附加字段col_order，您可以使用它来确定教师而不使用rownum 变量：

select s.col_entry,
  max(case when s.col_inquiry_name = 'Title' then s.col_value end) AS 'Title',
  max(case when s.col_inquiry_name = 'Course' then s.col_value end) AS 'Course',
  max(case when b.col_inquiry_name = 'Description' then b.col_value end) AS 'Description',
  max(case when d.col_inquiry_name = 'Semester' then d.col_value end) AS 'Semester',
  max(case when s.col_inquiry_name = 'Location' then s.col_value end) AS 'Location',
  max(case when s.col_inquiry_name = 'Teachers'
        and s.col_order = 1 then s.col_value end) AS 'Teachers_01',
  max(case when s.col_inquiry_name = 'Teachers'
        and s.col_order = 2 then s.col_value end) AS 'Teachers_02',
  max(case when s.col_inquiry_name = 'Teachers'
        and s.col_order = 3 then s.col_value end) AS 'Teachers_03',
  max(case when s.col_inquiry_name = 'Teachers'
        and s.col_order = 4 then s.col_value end) AS 'Teachers_04',
  max(case when s.col_inquiry_name = 'Teachers'
        and s.col_order = 5 then s.col_value end) AS 'Teachers_05'
from smallText s
left join bigText b
  on s.col_entry = b.col_entry 
left join date d
  on b.col_entry = d.col_entry 
group by s.col_entry

见SQL Fiddle with Demo

【讨论】：

哇，这太棒了。现在，可以在VIEW 中执行此操作吗？目前SELECT 在最后的JOIN 的FROM 子句中有一个SELECT，阻止它在视图中可用。
@user890857 我会考虑使用准备好的语句。
好吧，我需要使用视图而不是准备好的语句，因为这是内容管理系统的一部分。我正在尝试将分散在多个表中的数据重新格式化为单个视图，以便以更基本的每条目单行格式轻松访问它，以便前端设计人员可以从中提取数据这种观点真的很容易。
@user890857 几个问题，我知道你不能在视图中使用子查询，我认为你不能在 MySQL 视图中使用变量。我现在没有时间尝试重写这个，但是一个建议（虽然不是很好）是更新老师col_value 说Teacher_01 等。然后你不需要rownum 变量 - 见SQL Fiddle
感谢您在这方面帮助我。我看到更改 inquiry_name 可以使这更容易，但是如果该名称对于每一行保持相同，系统的其他部分会更好地工作。每个表都包含一个名为col_order 的行，我更新了sql fiddle 以展示它是如何工作的。我不确定是否有办法将该列用作生成各个教师列的方法。