如何截断计算列中的小数？

Question

我需要创建一个查询，以显示除第一本书以 0.01 的精度出版外，编辑了不止一本书的编辑的平均生产力 pages/day。

我现在显示了正确的列，但我需要减少 AverageProductivity 列中显示的零的数量。

要显示的列是

EditorName

BookName

计算列AverageProductivity

这是表格及其列

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)

示例数据

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');

我尝试使用格式语法来更改精度，但我不确定正确的语法。

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

有没有办法截断所有额外的零，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 函数实际上并没有改变数据类型，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))

另请注意，在转换为 DECIMAL 时，该值会自动四舍五入，因此您实际上不必调用 ROUND 函数（除非您想截断小数位）。

;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

您可以看到舍入值和小数值匹配（不是在比例和精度上，而是在内容上）。

如何截断计算列中的小数？

How do you truncate decimals in a computed column?

sql-server

precision

calculated-columns