0

对于下表,是否可以创建 SQL 语句来创建数据矩阵或视图?

桌子:

TeamA|TeamB|Won|Lost
--------------------
  A  |  B  | 5 | 3
  A  |  C  | 2 | 4
  A  |  D  | 9 | 1
  B  |  E  | 5 | 5
  C  |  A  | 2 | 4

结果矩阵:

     |  A | B |  C | D | E
----------------------------
  A  |  0 | 2 | -2 | 8 | 0
  B  |  0 | 0 |  0 | 0 | 0
  C  | -2 | 0 |  0 | 0 | 0
4

2 回答 2

1

您不能创建具有可变列数的 SQL 语句或视图。在标准 SQL 中,您可以通过执行以下操作来透视数据:

select TeamA,
       max(case when TeamB = 'A' then won - lost end) as A,
       max(case when TeamB = 'B' then won - lost end) as B,
       max(case when TeamB = 'C' then won - lost end) as C,
       max(case when TeamB = 'D' then won - lost end) as D,
       max(case when TeamB = 'E' then won - lost end) as E
from t
group by TeamA
order by 1

一些数据库支持数据透视语句。

通常,要执行此操作,您必须将 SQL 语句创建为字符串,然后执行它(通常称为动态SQL)。这样的语句可以由 SQL、存储过程、Excel 或其他一些编程工具生成。然后它需要被执行。

让我重复一遍:任何给定的 SQL 语句都有一组预定义的列。您不能改变列数。

于 2013-02-08T14:15:57.707 回答
1

有两种方法可以在 MySQL中透视数据。如果您提前知道值(团队),那么您将对值进行硬编码,或者您可以使用准备好的语句来生成动态 sql。

静态版本将是:

select TeamA,
  max(case when TeamB = 'A' then won - lost else 0 end) as A,
  max(case when TeamB = 'B' then won - lost else 0 end) as B,
  max(case when TeamB = 'C' then won - lost else 0 end) as C,
  max(case when TeamB = 'D' then won - lost else 0 end) as D,
  max(case when TeamB = 'E' then won - lost else 0 end) as E
from yourtable
group by TeamA;

请参阅带有演示的 SQL Fiddle

如果您想使用带有准备好的语句的动态版本,代码将是:

SET @sql = NULL;
SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'MAX(CASE WHEN TeamB = ''',
      TeamB,
      ''' THEN won - lost else 0 END) AS `',
      TeamB, '`'
    )
  ) INTO @sql
from
(
  select *
  from yourtable
  order by teamb
) x;

SET @sql 
  = CONCAT('SELECT TeamA, ', @sql, ' 
           from yourtable
           group by TeamA');

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

请参阅SQL Fiddle with Demo

编辑#1,在考虑到这一点之后,我实际上会稍微有点不同。我会生成一个真正的矩阵 os 数据,其中团队出现在行和列中。为此,您将首先使用UNION ALL查询来获取两列中的所有团队:

select teama Team1, teamb Team2,
  won-lost Total
from yourtable
union all
select teamb, teama,
  won-lost
from yourtable

请参阅SQL Fiddle with Demo。完成后,您将旋转数据:

select Team1,
  coalesce(max(case when Team2 = 'A' then Total end), 0) as A,
  coalesce(max(case when Team2 = 'B' then Total end), 0) as B,
  coalesce(max(case when Team2 = 'C' then Total end), 0) as C,
  coalesce(max(case when Team2 = 'D' then Total end), 0) as D,
  coalesce(max(case when Team2 = 'E' then Total end), 0) as E
from
(
  select teama Team1, teamb Team2,
    won-lost Total
  from yourtable
  union all
  select teamb, teama,
    won-lost
  from yourtable
) src
group by Team1;

请参阅SQL Fiddle with Demo。这给出了更详细的结果:

| TEAM1 |  A | B |  C | D | E |
-------------------------------
|     A |  0 | 2 | -2 | 8 | 0 |
|     B |  2 | 0 |  0 | 0 | 0 |
|     C | -2 | 0 |  0 | 0 | 0 |
|     D |  8 | 0 |  0 | 0 | 0 |
|     E |  0 | 0 |  0 | 0 | 0 |
于 2013-02-08T14:45:33.697 回答