Question

两部分问题：

在生成MySql的交叉表结果时，Distinct调用似乎不起作用......或者我错过了其他内容？我在几列中得到了相同的ClassName。即“MDC（介绍）”。
：SQLFiddle中的现有示例会产生结果（虽然不正确），但是当移动到托管的MySql时，它会失败并显示错误： #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'el FROM EnrollmentsTblx GROUP BY AutoNum' at line 1

SQL：

SET @sql = NULL;
SELECT
  GROUP_CONCAT(
    DISTINCT
    CONCAT(
      ' GROUP_CONCAT((CASE ClassName when ', CHAR(39), 
      ClassName, CHAR(39),
      ' then ', CHAR(39), DateCompleted, CHAR(39), ' else NULL END)) AS `',
      ClassName, '`'
    )
  ) INTO @sql
FROM EnrollmentsTbl;


SET @sql = CONCAT('SELECT AutoNum, UserName, ', @sql, ' 
              FROM EnrollmentsTbl 
              GROUP BY AutoNum, UserName');

SELECT @sql;
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

Schems：

SET NAMES 'UTF8';

CREATE TABLE `EnrollmentsTbl` (
`AutoNum` INTEGER PRIMARY KEY,
`UserName` VARCHAR(50),
`SubmitTime` DATETIME,
`ClassName` VARCHAR(50),
`ClassDate` DATETIME,
`ClassTime` VARCHAR(50),
`Enrolled` BOOLEAN,
`WaitListed` BOOLEAN,
`Instructor` VARCHAR(50),
`DateCompleted` DATETIME,
`Completed` BOOLEAN,
`EnrollmentsMisc` VARCHAR(50),
`Walkin` BOOLEAN
) CHARACTER SET 'UTF8';

INSERT INTO      `EnrollmentsTbl`(`AutoNum`,`UserName`,`SubmitTime`,`ClassName`,`ClassDate`,`ClassTime`,`Enrolled`,`WaitListed`,`Instructor`,`DateCompleted`,`Completed`,`EnrollmentsMisc`,`Walkin`)
VALUES(1,'John',NULL,'MDC (Intro)','2004-06-27 00:00:00',NULL,TRUE,FALSE,'Phil','2004-06-27 00:00:00',TRUE,NULL,FALSE),
  (2,'Bob',NULL,'MDC (Intro)','2004-06-27 00:00:00',NULL,TRUE,FALSE,'Phil','2004-06-27 00:00:00',TRUE,NULL,FALSE),
  (3,'Robert',NULL,'MDC (Intro)','2004-06-27 00:00:00',NULL,TRUE,FALSE,'Phil','2004-06-27 00:00:00',TRUE,NULL,FALSE),
  (4,'John','2010-08-04 06:11:10','HIPAA (Employee)','2010-08-04 00:00:00','6:12 AM',TRUE,FALSE,'On-line','2010-08-04 06:11:10',TRUE,NULL,FALSE),
  (5,'Debbie',NULL,'MDC (Intro)','2003-04-19 14:53:55',NULL,TRUE,FALSE,'devore','2003-04-19 14:53:55',TRUE,NULL,FALSE),
  (6,'Jeff',NULL,'MDC (Intro)','2003-03-29 14:26:23',NULL,TRUE,FALSE,'','2003-03-29 14:26:23',TRUE,NULL,FALSE),
  (7,'Tom',NULL,'Firehouse (Incident)','2004-07-13 00:00:00',NULL,TRUE,FALSE,'Shannon','2004-07-13 00:00:00',TRUE,NULL,FALSE),
  (8,'Janet','2016-06-30 14:02:05','MDC (On-Line)','2016-06-30 00:00:00','2:02 PM',TRUE,FALSE,'On-line','2016-06-30    14:02:05',TRUE,NULL,FALSE);

小提琴屏幕截图：

我在Access数据库中使用SQL作为SQL：

TRANSFORM DateCompleted
SELECT UserName
FROM EnrollmentsTbl
GROUP BY UserName
ORDER BY UserName
PIVOT ClassName

期望的结果如下所示：

UserName    MDC (Intro)     HIPAA (Employee)    Firehouse (Incident)
--------    -----------     ----------------    --------------------
John        6-27-2004       10-4-2006           8-6-2005
Bob         6-27-2004                           
Robert      6-27-2004                           8-6-2005
Debbie      4-19-2003
Jeff                                            11-25-2006
Tom                         7-13-2004
Janet                       11-25-2006

Answer 1

您的字符串在每个引号之前都有一个转义\。

为了证明这一点，我将它转储到文本编辑器（MySQL Workbench）中，在创建表格后很明显。我为查找和替换做了一个ctrl-H，（\＆＃39;到了＆＃39;），并且能够执行准备好的stmt并获得结果集。

在系统（或shell或各种编程语言）之间移动数据时，这是一个常见问题。我还注意到数据末尾有一些\n。

此外，DISTINCT适用于所有列（不是每个列）。

在两列输出上如此明显会导致以下容易：

class    student
-------  ----------
ABC      Drew
ABC      Barlay

查看mysql replace()函数，或者：

SELECT 
  GROUP_CONCAT(
    DISTINCT
    CONCAT(
      ' GROUP_CONCAT((CASE ClassName when \'',  
      ClassName,  
      '\' then \'',DateCompleted,'\' else NULL END)) AS `',
      ClassName, '`'
    )
  ) INTO @sql
FROM EnrollmentsTbl;
SET @sql = CONCAT("SELECT AutoNum, UserName, ", @sql, " FROM EnrollmentsTbl GROUP BY AutoNum, UserName");

select @sql;

呈现：

SELECT AutoNum, UserName,  GROUP_CONCAT((CASE ClassName when 'MDC (Intro)' then '2004-06-27 00:00:00' else NULL END)) AS `MDC (Intro)`, GROUP_CONCAT((CASE ClassName when 'HIPAA (Employee)' then '2010-08-04 06:11:10' else NULL END)) AS `HIPAA (Employee)`, GROUP_CONCAT((CASE ClassName when 'MDC (Intro)' then '2003-04-19 14:53:55' else NULL END)) AS `MDC (Intro)`, GROUP_CONCAT((CASE ClassName when 'MDC (Intro)' then '2003-03-29 14:26:23' else NULL END)) AS `MDC (Intro)`, GROUP_CONCAT((CASE ClassName when 'Firehouse (Incident)' then '2004-07-13 00:00:00' else NULL END)) AS `Firehouse (Incident)`, GROUP_CONCAT((CASE ClassName when 'MDC (On-Line)' then '2016-06-30 14:02:05' else NULL END)) AS `MDC (On-Line)` FROM EnrollmentsTbl GROUP BY AutoNum, UserName
-- Drew used above

像逃脱序列方面的魅力一样工作。

有关为什么在concat()上使用双引号的一点点了解，好吧，使用单引号导致@sql的prev值使用\转义其单引号因此可能会导致系统出现1064错误。因此，如果将字符串放在一起的第二部分，你可能已经无家可归了。

始终暂停并查看步骤之间的字符串，以查看状态是什么状态，以及未执行的操作。

现在谈谈你的DISTINCT数据问题（那是关于堆栈的新问题，而不是这里）

Answer 2

这似乎是我得到的最接近期望的结果，唯一的问题是它返回一个计数而不是完成的日期：

SELECT  `UserName`,
COUNT(
    CASE 
        WHEN `ClassName`='MDC (Intro)' 
        THEN `DateCompleted` 
        ELSE NULL 
    END
) AS 'MDC',
COUNT(
    CASE 
        WHEN `ClassName`='HIPAA(Employee)' 
        THEN `DateCompleted` 
        ELSE NULL 
    END
) AS 'HIPAA',
COUNT(
    CASE 
        WHEN `ClassName`='Firehouse (Incident)' 
        THEN `DateCompleted`
        ELSE NULL 
    END
) AS 'Firehouse'
FROM    EnrollmentsTbl
GROUP BY `UserName`;

SQLFiddle Example

示例来自：MySQL pivot table

Answer 3

不像我想要的那样动态，但根据需要进行了格式化。

解决：

SELECT  `UserName`,
    MAX(IF(`ClassName`='MDC (Intro)', `DateCompleted`, NULL)) AS 'MDC', 
    MAX(IF(`ClassName`='HIPAA (Employee)', `DateCompleted`, NULL)) AS 'HIPAA',
    MAX(IF(`ClassName`='MDC (On-Line)', `DateCompleted`, NULL)) AS 'MDC-OL',
    MAX(IF(`ClassName`='Firehouse (Incident)', `DateCompleted`, NULL)) AS 'Fierhouse'
FROM    EnrollmentsTbl
GROUP BY `UserName`;

工作示例： SQLFiddle

MySQL CrossTab结果包含非不同的列

3 个答案: