在SQL Server 2005中"select*from table"vs"select colA,colB,etc from table"

Question

为一篇冗长的帖子道歉,但我需要发布一些代码来说明问题.

灵感来自问题*什么是不使用选择的原因？,我决定指出一些我之前注意到的select*行为的观察结果.

让我们的代码说明一切:

IF  EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[starTest]') AND type in (N'U'))
DROP TABLE [dbo].[starTest]
CREATE TABLE [dbo].[starTest](
    [id] [int] IDENTITY(1,1) NOT NULL,
    [A] [varchar](50) NULL,
    [B] [varchar](50) NULL,
    [C] [varchar](50) NULL
) ON [PRIMARY]

GO

insert into dbo.starTest(a,b,c)
select 'a1','b1','c1'
union all select 'a2','b2','c2'
union all select 'a3','b3','c3'

go
IF  EXISTS (SELECT * FROM sys.views WHERE object_id = OBJECT_ID(N'[dbo].[vStartest]'))
DROP VIEW [dbo].[vStartest]
go
create view dbo.vStartest as
select * from dbo.starTest
go

go
IF  EXISTS (SELECT * FROM sys.views WHERE object_id = OBJECT_ID(N'[dbo].[vExplicittest]'))
DROP VIEW [dbo].[vExplicittest]
go
create view dbo.[vExplicittest] as
select a,b,c from dbo.starTest
go


select a,b,c from dbo.vStartest
select a,b,c from dbo.vExplicitTest

IF  EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[starTest]') AND type in (N'U'))
DROP TABLE [dbo].[starTest]
CREATE TABLE [dbo].[starTest](
    [id] [int] IDENTITY(1,1) NOT NULL,
    [A] [varchar](50) NULL,
    [B] [varchar](50) NULL,
    [D] [varchar](50) NULL,
    [C] [varchar](50) NULL
) ON [PRIMARY]

GO

insert into dbo.starTest(a,b,d,c)
select 'a1','b1','d1','c1'
union all select 'a2','b2','d2','c2'
union all select 'a3','b3','d3','c3'

select a,b,c from dbo.vExplicittest
select a,b,c from dbo.vStartest

如果执行以下查询并查看最后2个select语句的结果,您将看到的结果如下:

select a,b,c from dbo.vExplicittest
a1  b1  c1
a2  b2  c2
a3  b3  c3

select a,b,c from dbo.vStartest
a1  b1  d1
a2  b2  d2
a3  b3  d3

正如您在dbo.vStartest中选择a,b,c的结果中所看到的,列c的数据已被colum d中的数据替换.

我认为这与编译视图的方式有关,我的理解是列由列索引(1,2,3,4)映射而不是名称.

我想我会发布它作为警告,让人们在SQL中使用select*并遇到意外行为.

注意:如果在每次修改表后重建使用select*的视图,它将按预期工作.

Answer 1

sp_refreshview用于修复视图,或在视图定义中使用WITH SCHEMABINDING

如果未使用SCHEMABINDING子句创建视图,则应在对视图下方影响视图定义的对象进行更改时运行sp_refreshview.否则,查询时视图可能会产生意外结果.