T-SQL 替换函数缺少一些使用 nvarchar(max) 的匹配项

Question

给定以下 T-SQL 代码：

declare @lf char(1) set @lf = char(10);
declare @cr char(1) set @cr = char(13);

select  replace(isnull(note,''), @cr+@lf,@lf)  from T

在某些情况下，@cr+@lf 在note 列中不是每次出现都会被@lf 替换？

我正在尝试对确实发生这种情况的情况进行故障排除。

note 列定义为nvarchar(max)。 documentation 说：

如果 string_expression 不是 varchar(max) 或 nvarchar(max) 类型，REPLACE 会在 8,000 字节处截断返回值。要返回大于 8,000 字节的值，必须将 string_expression 显式转换为大值数据类型。

如果我理解正确，则无需强制转换，因为 note 已经是允许返回值大于 8000 字节的正确数据类型。

我想也许isnull 函数没有返回nvarchar(max) 但documentation 说它返回被测试值的类型：

...返回类型
返回与 check_expression 相同的类型。

并且返回的值没有被截断；只是有些crlf对被忽略了。

我一定是忽略了什么。

declare @t table( notes nvarchar(max));

insert @t(notes)
values
(
'From: kkkkkkk@aaaaaaaaa.com <kkkkkkk@aaaaaaaaa.com> 
Sent: Monday, May 00, 0008 00:55 PM
To: Jan Zzzz <sZzzz@dddd.dd.com>
Subject: RE: [Secure Message] aaaaaaaaa ABC ddddddddddddd--XXXXX-X

Hi Jan, 

The ddddddddddddd is valid for one year.  I have attached the Zzzzzzz Rrrrrrrr which you will find behind the  blank cover page and ddddddddddddd form.  Please let me know if this is what you need.  

Best Regards, 

Yyyyyy 

Kkkkkkkk Kkkkkk, ABC, DEF
ABC Mmmmmmmm
P 800.007.0000 ext 000 | F 600.000.0070 



Electronic mail is not considered to be a secure form of communication for Protected Health Information. If you are concerned about privacy, please call aaaaaaaaa directly at 0-800-007-0000. If you would like to review our privacy policy, it can be found on our website: www.ddddddddddddd.com.

This email, including any attached files, may contain confidential and privileged information for the sole use of the intended recipient(s). Any review, use, distribution or disclosure by others is strictly prohibited. If you are not the addressee indicated in this message (or authorized to receive information for the recipient), please contact the sender by reply e-mail and delete all copies of this message (including any attachments).

From: Jan Zzzz <sZzzz@dddd.dd.com> 
Sent: Monday, May 00, 0008 8:56 AM
To: Kkkkkkkk Kkkkkk <kkkkkkk@aaaaaaaaa.com>; Jan Zzzz <sZzzz@dddd.dd.com>
Subject: Re: [Secure Message] aaaaaaaaa ABC ddddddddddddd--XXXXX-X

Hi, this expired, I need a copy of the aaaaaaa aaaa so I can submit my aaaaaaa aaa aaaaaaaa. Thank you. SZzzz

On 0/00/0008 8:00 AM, Jan Zzzz wrote:
Thank you for the dddddddd, I am mmmmmmm mmm today.

On 0/0/0008 6:05 PM, Kkkkkkkk Kkkkkk wrote:

[Secure Message] aaaaaaaaa ABC ddddddddddddd--XXXXX-X    

Kkkkkkkk Kkkkkk has sent you a secure message.
Subject:    aaaaaaaaa ABC ddddddddddddd--XXXXX-X
From:   Kkkkkkkk Kkkkkk <kkkkkkk@aaaaaaaaa.com>

To: Jan Zzzz <sZzzz@dddd.dd.com>

Expires:    May 00, 0008

View Secure Message 



Note: If you have any concerns about the authenticity of this message please contact the original sender directly.'   
)

select notes from @t;
select replace(notes, char(13),'') from @t;

Answer 1

如果@cr+@cr+@lf 出现在note 中，您将在SELECT 中留下@cr+@lf，除非您需要@cr，当它自己出现时，您可能最好这样做：

declare @cr char(1) set @cr = char(13);

select  replace(isnull(note,''), @cr,'')  from T

Answer 2

如果它只是一行，应该这样做，将它们全部删除并放回去

set @note =  replace(replace(isnull(@note,''),@cr,''),@lf,'')+@lf . //or whatever line endings you want

如果它的多行尝试这样的事情

declare @note as nvarchar(max)
declare @lf char(1) set @lf = char(10);
declare @cr char(1) set @cr = char(13);

set @note = 'A'+char(10)+char(13)+char(10)+char(13)+char(10)+char(13)+char(10)+char(13)+'A'+char(10)+char(13)

set @note = replace(isnull(@note,''),@cr,'')

--not sure if you want to keep all the user lf's but if you want only one try this?
if (patindex(isnull(@note,''),@lf+@lf) >= 0)
begin
set @note = replace(isnull(@note,''),@lf+@lf,@lf)
end 

select @note
select cast(@note as VARBINARY(100))
select len(@note)

Answer 3

每种情况都会被替换，但您可能会通过替换创建一些 CrLfs。请参阅下面的示例以及如何缓解它。

DECLARE @Cr CHAR(1)=CHAR(13)
DECLARE @Lf CHAR(1)=CHAR(10)
DECLARE @CrLf CHAR(2)=CHAR(13)+CHAR(10)
DECLARE @NoteTbl TABLE(Note NVARCHAR(MAX))
INSERT INTO @NoteTbl (Note) SELECT @Cr + @CrLf

--example can result in CrLF being created
SELECT [NewNote],LEN([NewNote]) FROM (SELECT replace(isnull(note,''), @CrLf,@lf) AS [NewNote] FROM @NoteTbl) AS a

--Option 1: Replace all Cr with nothing; this is effectively the same as replacing CrLf with Lf
SELECT [NewNote],LEN([NewNote]) FROM (SELECT replace(isnull(note,''), @Cr,'') AS [NewNote] FROM @NoteTbl) AS a

--Option 2: insert the notes into a table and loop until CrLf is gone, this might be useful if you need to do multiple different  data scrubs
DECLARE @NotesCleaned TABLE(Note NVARCHAR(MAX))
INSERT INTO @NotesCleaned (Note) SELECT Note FROM @NoteTbl
WHILE EXISTS(
    SELECT * FROM @NotesCleaned WHERE Note Like '%' + @CrLf + '%'
)
    BEGIN
        UPDATE @NotesCleaned SET Note=replace(isnull(note,''), @CrLf,@lf)
    END

SELECT Note,LEN(Note) FROM @NotesCleaned 

Answer 4

我相信我可能已经找到了部分答案。在 SSMS 中：

Tools->Options->SQL Server->Results to Grid

[ x ]  Retain CR/LF on copy or save

实际上会恢复您对 replace() 的调用已删除的 CR。