Question

我得到了“学生”表格，如下所示：

ReposeBuffer

我正在尝试旋转桌子但没有得到它。

我也在Stackoverflow中进行了搜索，但是我认为期望的输出是不同的，所以找不到合适的查询。

这是预期的输出：

student    |        section
-----------+-----------------
john       |        Ace
jack       |        Newbie
kiya       |        Top
BRET       |        Top
Scott      |        Top
Stephen    |        Ace
Fran       |        Ace
Chris      |        Good
Kathleen   |        Good
Rick       |        Newbie

Answer 1

使用条件聚合：

SELECT 
    MAX(CASE WHEN section = 'Ace' THEN student END) Ace,
    MAX(CASE WHEN section = 'Top' THEN student END) Top,
    MAX(CASE WHEN section = 'Newbie' THEN student END) Newbie,
    MAX(CASE WHEN section = 'Good' THEN student END) Good
FROM students
GROUP BY student
ORDER BY student

如果您实际上想在没有匹配项而不是'N/A'值的情况下在结果集中看到NULL，请使用COALESCE()（或RDBMS的等效项）：

SELECT 
    COALESCE(MAX(CASE WHEN section = 'Ace' THEN student END), 'N/A') Ace,
    COALESCE(MAX(CASE WHEN section = 'Top' THEN student END), 'N/A') Top,
    COALESCE(MAX(CASE WHEN section = 'Newbie' THEN student END), 'N/A') Newbie,
    COALESCE(MAX(CASE WHEN section = 'Good' THEN student END), 'N/A') Good
FROM students
GROUP BY student
ORDER BY student

我不知道如何使用数据透视功能转换表格

1 个答案: