为什么我的计算列中的数据显示为 null / 0 值

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，但计算列未显示任何计算平均值。

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');

这是查询...

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 服务器做整数除法。所以，1/2 是 0，而不是 0.5。

您可以轻松地在您的代码中解决这个问题。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，解决了整数除法问题。

为什么我的计算列中的数据显示为 null / 0 值

Why is the Data in my Computed Columns showing up with null / 0 values

sql

tsql

sql-server

calculated-columns