我希望转换Table1中的数据,如Pivot_table中数据的第一张图片所示.有可能在MySQL中这样做吗？因为数据透视表(A,B,C,D)的值是varchar数据格式,我不能像SUM那样使用MySQL的任何聚合函数.

Table1:
PK        Name     Subject     Grade
-------------------------------------
1         Bob       Math        A
2         Bob       History     B
3         Bob       Language    C
4         Bob       Biology     D
5         Sue       History     C
6         Sue       Math        A
7         Sue       Music       A
8         Sue       Geography   C


Pivot_table:
Subject     Bob     Sue
-------------------------
Math        A        A
History     B        C
Language    C 
Biology     D
Music                A
Geography            C

谢谢你的帮助

解决方法:

静态查询(仅涉及Bob和Sue)可能如下所示

SELECT subject, 
       MAX(CASE WHEN name = 'Bob' THEN grade END) `Bob`,
       MAX(CASE WHEN name = 'Sue' THEN grade END) `Sue` 
  FROM table1 
 GROUP BY subject

现在能够考虑其他名称使用像这样的动态SQL

SET @sql = NULL;

SELECT GROUP_CONCAT(DISTINCT
         CONCAT('MAX(CASE WHEN name = ''', name,
                ''' THEN grade END) `', name, '`'))
  INTO @sql
  FROM table1;

SET @sql = CONCAT('SELECT subject, ', @sql, ' 
                     FROM table1 
                    GROUP BY subject');

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

输出：

|   SUBJECT |    BOB |    SUE |
|-----------|--------|--------|
|   Biology |      D | (null) |
| Geography | (null) |      C |
|   History |      B |      C |
|  Language |      C | (null) |
|      Math |      A |      A |
|     Music | (null) |      A |

这是SQLFiddle演示

您可以将其包装到存储过程中以简化调用端的操作

DELIMITER $$
CREATE PROCEDURE sp_grade_report()
BEGIN
  SET @sql = NULL;

  SELECT GROUP_CONCAT(DISTINCT
           CONCAT('MAX(CASE WHEN name = ''', name,
                  ''' THEN grade END) `', name, '`'))
    INTO @sql
    FROM table1;

  SET @sql = CONCAT('SELECT subject, ', @sql, ' 
                       FROM table1 
                      GROUP BY subject');

  PREPARE stmt FROM @sql;
  EXECUTE stmt;
  DEALLOCATE PREPARE stmt;
END$$
DELIMITER ;

样品用法：

CALL sp_grade_report();

这是SQLFiddle演示