将行作为列透视-评级数据库

Question

我有以下表格：

评分

User-ID     ISBN    Book-Rating
244662  0373630689  3
19378   0812515595  2
238625  0441892604  5
180315  0140439072  1
242471  3548248950  1

BOOKS ISBN Book-Title Book-Author Year-Of-Publication Publisher 0393000753 A Reckoning May Sarton 1981 WW Norton

使用MySQL，我想创建一个如下表：

----- User1 User2 User3 ... ISBN1 Rating11 NaN Nan ISBN2 NaN Rating21 Rating23 ISBN3 Rating31 NaN NaN ...

我已经了解了如何在固定数量的列上执行此操作 。 但是如何将行转换为列呢？ 我已经尝试过类似的东西

create view BX-Book-Ratings-Extended as ( select ISBN , case when Book-Rating = "1" then 1 end as User-ID = "1" then 1 end as , case when Book-Rating = "2" then 2 end as User-ID的, case when = "2" then 2 end as , case when Book-Rating = "3" then 3 end as User-ID = "3" then 3 end as , case when Book-Rating = "4" then 4 end as User-ID = "4" then 4 end as , case when Book-Rating = "5" then 5 end as End-ID from BX -书评)

这不起作用-视图为空...我也试图从另一个线程采用解决方案，但不断收到语法错误，我无法识别：

SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'ifnull(SUM(case when `Book-Rating` = ''',
      `User-ID`,
      ''' then `Book-Rating` end),0) AS ',
      `User-ID`
    )
  ) INTO @sql
FROM
  `BX-Book-Ratings`;
SET @sql = CONCAT('SELECT ISBN, ', @sql, ' 
                  FROM BX-Book-Ratings 
                   GROUP BY ISBN');

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

数据集在这里 。

感谢您的任何建议！

Answer 1

您第二次使用动态SQL（准备/执行）的尝试已结束。
试试这个查询：

SET @sql = NULL;

SELECT Concat(
         'SELECT ISBN, ',
         Group_Concat( x SEPARATOR ','),
         ' FROM ratings GROUP BY ISBN '
       )
INTO @sql
FROM (
  SELECT Concat('Max( CASE WHEN User_ID = ', 
                User_ID, 
               ' THEN Book_Rating END ) As User_', 
               User_ID 
         ) As x
  FROM ratings 
  GROUP BY User_ID
  ORDER BY User_ID
) x;

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

演示： http ： //rextester.com/GLJV4738

如果一个用户可以为一本书获得更多评分，则将max替换为sum 。

---

不幸的是，由于MySql的限制，该解决方案不应该为超过数千名用户（列）工作

• MySQL对每个表的硬限制为4096列（因此查询结果集也不能超过4096列）
• MySQL表的最大行大小限制为65,535字节（ 此处有更多信息 ），因此，行中的150.000用户必须确保超过65 k字节