sql - 如何使用 SQLite 将值转换为列？

Question

我用这段代码创建了一个名为 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的流派计数，而不是因为 Label 列而重复计算。我想要这个:

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

因为你不能使用pivot，所以你可以这样做。

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