可为NULL 但不能重复的SQL约束
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER trigger [dbo].[checkExamNo] on [dbo].[student]
for insert,update as
if exists(select examNo from student where isnull(examNo ,'')<>'' group by examNo having count(*)>1 )
rollback
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系统环境：Windows 7
软件环境：Visual C++ 2008 SP1 +SQL Server 2005
本次目的：编写一个航空管理系统
这是数据库课程设计的成果，虽然成绩不佳，但是作为我用VC++ 以来编写的最大程序还是传到网上，以供参考。用VC++ 做数据库设计并不容易，但也不是不可能。以下是我的程序界面，后面 ......
1.ORACLE采用自下而上的顺序解析WHERE子句,根据这个原理,表之间的连接必须写在其他WHERE条件之前, 那些可以过滤掉最大数量记录的条件必须写在WHERE子句的末尾.
(低效)
SELECT … from EMP E WHERE SAL > 50000 AND JOB = ‘MANAGER’ AND 25 < (SELECT COUNT(*) from EMP WHERE MGR=E. ......
select batch_no "批次号",get_id "分类" from (
select(
select plan1.batch_no from product_plan plan1 where plan1.item_no=(select head1.product_code from wo_head head1 where head1.order_no =bbb)) batch_no,
(select decode(get_id,'BUY','外购件','MAK','自制件','MB','未定') from item where item_ ......
SQL Server连接远程数据源的基本方法有下面三种：
OPENDATASOURCE: The OPENDATASOURCE function is used to specify connection information for a remote data source by specifying the OLE DB provider and an initialization string. OPENDATASOURCE can be used directly within a SELECT, INSERT, UPDATE, or DELET ......
