Question

我有一个表Books，其中包含一本书的发行年份列（类型：年份）。我想计算每十年发布的书籍数量。

我尝试了以下内容：

select count(*) as count, concat(decade, '-', decade + 9) as ReleaseYear
from (
    select floor('ReleaseYear' / 10) * 10 as decade
    from Book
) t
group by decade;

但它返回0结果。

当我尝试year('ReleaseYear')时，它会返回空值。

Answer 1

为每一行创建一个decade值，并按十年来查找计数（十年）。

<强>查询

select t.decade,count(t.decade) as BooksCount from
(
    select *,
    concat((releaseYear - ((releaseYear % 10)-1)),'-',((releaseYear - ((releaseYear % 10)-1))+ 9)) as decade
   from Books
)t
group by t.decade;

SQL Fiddle

Answer 2

尝试;

SELECT 
    count(*) `count`,
    concat(FLOOR(year(`ReleaseYear`)/10)*10, '-', FLOOR(year(`ReleaseYear`)/10)*10  +  9) `ReleaseYear`
from `books`
group by FLOOR(year(`ReleaseYear`)/10)*10

演示 sqlfiddle

根据数十年计算数据

2 个答案: