如何使用 SQLite 将值转入列中？

Question

我用以下代码制作了一个名为tbl的表：

CREATE TABLE tbl
    (
      `Year` int, 
      `Album` varchar(255),
      `Artist` varchar(255),
      `Label` varchar(255),
      `Genre` varchar(255),
      `id` int
    )
;

INSERT INTO tbl
    (
      `Year`,
      `Album`,
      `Artist`,
      `Label`,
      `Genre`,
      `id`
    )
VALUES
    (1990, "Greatest Hits", "The Best", "Least Def", "hip hop", 123),
    (1990, "Greatest Hits", "The Best", "Roofless", "hip hop", 123),
    (1990, "4-Boyz", "3 Guyz", "Pacific", "pop-dance", 23),
    (1990, "4-Boyz", "3 Guyz", "Atlantic", "pop-dance", 23)
;

我想运行一个查询来显示每年流派的数量，而不会因为Label列而重复计算。 我要这个：

Year, hip hop, pop-dance
1990, 1, 1

我必须运行什么查询才能得到我想要的？

Answer 1

因为您不能使用pivot ，所以您可以这样做。

select year,
count(distinct case when `Genre` = 'hip hop' then 1 end) as hiphop,
count(distinct case when `Genre` = 'pop-dance' then 1 end) as popdance
from tbl
group by year

Answer 2

接受的答案对我有用。

我在这里添加了一个更复杂的案例，如果有人需要，加入。

也可以看看：

将两个 SQL 查询的结果组合为单独的列

我的例子：

    select Info.*, Roots.*, ColeColeFit.*, f10.*, f20k.*
    from Info
    join (select * from Data where Frequency = 10) as f10
      on f10.Info_ID = Info.id
    join (select * from Data where Frequency = 20000) as f20k
      on f20k.Info_ID = Info.id
    join Roots
      on Info.File_Num = Roots."Plant number"
    join ColeColeFit
      on ColeColeFit.id = Info.id