为什么我的计算列中的数据显示为null / 0值[重复]

Question

此问题已经在这里有了答案：

• SQL Server, division returns zero6个答案
• why does sql server return 0 for 1 / 2?1个答案
• Division of integers returns 02个答案

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。

我现在显示正确的列，但计算的列未显示任何计算的平均值。

要显示的列是

EditorName

BookName

计算列AverageProductivity

这里是表及其列

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');

这里是查询...

select * from (
    select 
    e.EditorName,
    b.BookName,
    round(
        NoOfPages/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

结果...

Melanie eRobot  0
Melanie An Uncle's Letters  0
George  Pretty flowers  0

Answer 1

SQL Server执行整数除法。因此，1/2是0，而不是0.5。

您可以在代码中轻松修复此问题。我认为最简单的方法是：

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

* 1.0将其转换为带小数位的数字，解决了整数除法的问题。