How do I pivot values into columns with SQLite?

问题:

I made a table called tbl with this code:

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)
;

I want to run a query to show me the count of genres for each year, without double counting because of the Label column. I want this:

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

What query must I run to get what I want?

回答1:

Because you can't use pivot, you can do this.

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

回答2:

The accepted answer worked for me.

I add here a more complex case, with join, in case someone needs.

see also:

Combining 2 SQL queries and getting result set in one

my example:

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