如何添加和删除但应保留记录

问题描述

我正在图书馆项目中工作.
我有两种形式，即frmBooks和frmIssueRegister
和表格书籍和问题
我在表格中的字段是:Totalcopies，IssuedCopies，LeftCopies
当我发行一本书(frmIssueRegister)并保存时，应该
在frmBooks中进行以下更改:
总份数= 10
已发行副本= 3
库中的左副本= 7

类似地，在归还我的书时，应减去:
总份数= 10
已发行副本= 2
库中的左副本= 8

请帮我!!!!!!

I m working in a library project.
I have two forms i.e frmBooks and frmIssueRegister
and tables books and Issue
My fields in table books are : Totalcopies, IssuedCopies,LeftCopies
when I m issuing a book (frmIssueRegister)and on saving it should
do the following changes in frmBooks:
Total copies= 10
Issued copies=3
Left Copies in library = 7

similarly on returning i book ,it should subtract:
Total copies= 10
Issued copies=2
Left Copies in library = 8

Please help me out !!!

推荐答案

SELECT TotalCopies,
       IssuedCopies,
       TotalCopies - IssuedCopies AS CopiesLeft
FROM ...

最好不要使用已存储的计算字段(至少以可以修改的方式).

It''s a good rule of thumb that calculated fields should never be store (at least in a way that they can be modified).

update frmIssueRegister set Issuedcopies=Issuedcopies+1,leftCopies=leftCopies-1 where bookid='123'

希望对您有帮助

hope it will helps you

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