Question

我需要创建一个查询，以显示从事多于一本书的编辑的平均生产力，除了第一本书的出版精度为每天0.01页。

我现在显示的列正确，但是我需要减少AverageProductivity列中显示的零。

要显示的列是

EditorName

BookName

计算列AverageProductivity

这是表及其列

AGENT  AgentID (PK,varchar(11), not null)
       AgentName (varchar(25), not null)

BOOK   BookName (PK, varchar(45), not null)
       Genre (varchar(25), not null)
       DateOfPublication (date, not null)
       NoOfPages (int, not null)
       WriterID (PK, FK,, varchar(11), not null)
       EditorID (FK, varchar(11), not null)

EDITOR EditorID (PK, varchar(11), not null)
       EditorName (varchar(25), not null)
       Mentors_EditorID (FK, varchar(11), null)

WRITER WriterID (PK, varchar(11), not null)
       WriterName (varchar(25), not null)
       AgentID (FK, varchar(11), not null)

样本数据

insert into BOOK (BookName, WriterID, Genre, DateOfPublication, NoOfPages, EditorID)
values ('Valley of Heroes','10','Fiction','2010-01-12',874,'20');
insert into BOOK (BookName, WriterID, Genre, DateOfPublication, NoOfPages, EditorID)
values ('The Ruler''s Return','11','Fantasy','2012-03-14',765,'22');
insert into BOOK (BookName, WriterID, Genre, DateOfPublication, NoOfPages, EditorID)
values ('eRobot','11','Fantasy','2011-04-15',264,'20');
insert into BOOK (BookName, WriterID, Genre, DateOfPublication, NoOfPages, EditorID)
values ('An Uncle''s Letters','12','Fiction','2012-06-12',258,'20');
insert into BOOK (BookName, WriterID, Genre, DateOfPublication, NoOfPages, EditorID)
values ('Pretty flowers','13','Album','2013-01-31',148,'22');
insert into BOOK (BookName, WriterID, Genre, DateOfPublication, NoOfPages, EditorID)
values ('A Tale of Lions','12','Fantasy','2012-08-17',301,'21');
insert into BOOK (BookName, WriterID, Genre, DateOfPublication, NoOfPages, EditorID)
values ('eRobot','13','Sci Fi','2012-10-04',465,'23');

我试图使用格式语法来更改精度，但是我不确定该语法是否正确。

这是查询...

use SignumLibri_01
select * from (
    select e.EditorName, b.BookName,
       round(NoOfPages * 1.0
                 / datediff(day, lag(b.DateOfPublication)
                                   over (partition by b.EditorID
                                           order by b.DateOfPublication
                                         )
                               ,DateOfPublication
                            )
               , 2) AverageProductivity       
   from book b
   inner join editor e on e.EditorID = b.EditorID 
) x
where AverageProductivity is not null

有没有一种方法可以截断所有多余的零，所以我必须达到0.00的精度？

结果...

Melanie eRobot  0.580000000000
Melanie An Uncle's Letters  0.610000000000
George  Pretty flowers  0.460000000000

Answer 1

您需要将数据类型更改为DECIMAL(X, 2)。 ROUND函数实际上并不会改变数据类型，只是从特定位置开始截断或舍入值。

CONVERT(
    DECIMAL(10, 2),
    round(NoOfPages * 1.0 /datediff(
            day, 
            lag(b.DateOfPublication) over(partition by b.EditorID order by b.DateOfPublication),
            DateOfPublication),
        2))

还请注意，在转换为DECIMAL时，该值会自动舍入，因此实际上不必调用ROUND函数（除非要截断小数）。

;WITH ValueWithDecimals AS
(
    SELECT
        Value = 50 * 1.0 / 19
)
SELECT
    Original = V.Value,
    RoundedAt2 = ROUND(V.Value, 2),
    RoundedAt4 = ROUND(V.Value, 4),
    ConvertedToDecimal2 = CONVERT(DECIMAL(10, 2), V.Value),
    ConvertedToDecimal4 = CONVERT(DECIMAL(10, 4), V.Value)
FROM
    ValueWithDecimals AS V

结果：

Original    RoundedAt2  RoundedAt4  ConvertedToDecimal2 ConvertedToDecimal4
2.631578    2.630000    2.631600    2.63                2.6316

您会看到四舍五入的值和十进制值匹配（不是按比例和精度，而是按内容）。

如何截断计算列中的小数？

1 个答案: