可以进行这样的查询吗？

Question

我在mySQL db上有一个这样的表：

Olimpiade     Sport        Disciplina   Categoria
---------------------------------------------------
London 2012   Athletics    100m         men
London 2012   Athletics    100m         woman
Beijing 2008  Athletics    200m         men
Beijing 2008  Athletics    200m         women
Athens 2004   Athletics    800m         men
Athens 2004   Athletics    800m         women

诸若此类。我不知道是否可以设置这样的查询，但我希望得到的结果如下：

Disciplina   Categoria   London 2012    Beijing 2008   Athens 2004
------------------------------------------------------------------
100m         men         yes            no             yes
100m         women       yes            yes            no
200m         men         yes            no             yes
200m         women       yes            yes            no
800m         men         yes            yes            yes
800m         women       yes            yes            yes

那就是奥运会版本的试验是否存在。

Answer 1

是的，你可以，像这样用例，

Select Disciplina, Categoria, 
CASE when Olimpiade = 'London 2012' then 'yes' else 'no' end as 'London 2012', 
CASE when Olimpiade = 'Beijing 2008' then 'yes' else 'no' end as 'Biejing 2008',
CASE when Olimpiade = 'Athens 2004' then 'yes' else 'no' end as 'Athens 2004'    from tableName group by Disciplina, Categoria order by Disciplina, Categoria

Answer 2

您可以使用内部select构建查询。内部select通过添加列来准备数据。外部select将数据分组：

SELECT
    Disciplina,
    Categoria,
    IF (MAX(`London 2012`) > 0, 'yes', 'no') AS 'London 2012',
    IF (MAX(`Beijing 2008`) > 0, 'yes', 'no') AS 'Beijing 2008',
    IF (MAX(`Athens 2004`) > 0, 'yes', 'no') AS 'Athens 2004'
FROM
    (
        SELECT 
            Disciplina, 
            Categoria, 
            IF (Olimpiade = 'London 2012', 1, 0) AS 'London 2012',
            IF (Olimpiade = 'Beijing 2008', 1, 0) AS 'Beijing 2008',
            IF (Olimpiade = 'Athens 2004', 1, 0) AS 'Athens 2004'
        FROM YourTableName
    ) AS Games
GROUP BY Disciplina, Categoria
ORDER BY Disciplina, Categoria

您必须将YourTableName替换为您的表名。