Table 名称包含字符 0xFFFF 有效标识符

Question

有关 differences Between Compatibility Level 80 and Level 90 的 MS 文档说明了兼容级别 80，"Object names containing the character 0xFFFF are valid identifiers"，但是字符 0xFFFF 可以将对象名称命名为 table 名称，.. .?

能不能帮帮忙，谢谢！

Answer 1

您的数据库极不可能包含任何 table 或其他具有此字符标识符的对象。话虽如此，这是可以做到的。我使用 SQL Server 2008 来运行以下脚本：

create database TestFFFF
go
alter database TestFFFF set compatibility_level = 80
go
use TestFFFF

declare @s nvarchar(200)

-- Build a string that will create a table
-- In our first example, we'll use a simple character
-- nchar(65) is the same as capital letter 'A'
-- so this will create a table named tungnAguyen.

set @s = N'create table [tungn' + NCHAR(65) + N'guyen] ( IDA int )'
exec sp_executesql @s

-- Now we will create a table name with character U+FFFF.
-- Note 65535 is decimal for hexadecimal FFFF.
-- Note this will only work if the database compatibility level is 80 or less.
-- Otherwise you'll get an error message.

set @s = N'create table [tungn' + NCHAR(65535) + N'guyen] ( IDF int )'
exec sp_executesql @s

-- Let's see if it worked.
-- I'll convert the table name to hexadecimal so you can see each character.

select name, CAST(name as varbinary(1000)) as BinName 
from sysobjects where name like N'tun%'

-- The result looks like this:
-- name        BinName                                    
-- tungnAguyen 0x740075006E0067006E00410067007500790065006E00
-- tungnguyen  0x740075006E0067006E00FFFF67007500790065006E00
--
-- The first row shows the first table we created using letter 'A'.
-- In the hexidecimal version you see 4100 in the middle.  That's the 'A'
-- 
-- In the second row, there appears to be nothing in the middle
-- of the name.
-- The reason is that character FFFF is not printable. 
-- In the middle of the hexidecimal you see FFFF.  This is proof
-- that the identifier contains that character.
--
-- Let's see if we can access these tables.
-- Start with the table that contains letter 'A'

set @S = N'select * from [tungn' + NCHAR(65) + N'guyen]'    
exec sp_executesql @S

-- It works. 
-- We've not inserted any rows, so the result is empty, but it works.
-- Now let's access the other table.

set @S = N'select * from [tungn' + NCHAR(65535) + N'guyen]'    
exec sp_executesql @S

-- This works too, as long as we are using compatibility level 80.
-- Let's change the compatibility level to 90 
-- and see what happens.

go
alter database TestFFFF set compatibility_level = 90
go

declare @S nvarchar(200)
set @S = N'select * from [tungn' + NCHAR(65535) + N'guyen]'
exec sp_executesql @S

-- This time it fails. We get an error message:
-- Msg 1055, Level 16, State 1, Line 73
-- 'tun...' is an invalid name because it contains 
-- a NULL character or an invalid unicode character.
--
-- The U+FFFF is the invalid Unicode character it is talking
-- about.  According to the Unicode standard there is 
-- no such character.

Table 名称包含字符 0xFFFF 有效标识符

Table names containing the character 0xFFFF valid identifiers

sql

sql-server

sql-server-2005