SQL 替换空 xml 值

Question

我是sql的初学者，我不知道如何找到解决问题的方法。

我有一个包含项目的表，一列包含 xml 值。我想检查字段是否存在并更新它。

我找到了一种修改现有 xml 值的方法，但是当它为 NULL 时它不起作用

有我的代码：

SELECT @xml=IDA_Xml,
@isData = IDA_Xml.exist('(/Root/Data[1]/text())[1]')
FROM DATA
WHERE IDA_UId=@guid
If (@xml is NULL)
BEGIN
-- Create a xml value with <Root></Root>
-- It will be update later
-- set isData to 0
END
IF (@isData = 0)
UPDATE ItemData SET IDA_Xml.modify
('
insert <Data Name = "Info">{sql:variable("@number")}</Data>
into (/Root/*)[1]
')
WHERE IDA_UId = @guid;
ELSE
UPDATE ItemData SET IDA_Xml.modify
('
replace value of (/Root/Data[1]/text())[1]
with    sql:variable("@number")
')
WHERE IDA_UId = @guid;

Answer 1

在这种情况下，在大多数情况下，最简单的方法是丢弃现有元素并将其作为新元素插入：

DECLARE @mockup TABLE(ID INT IDENTITY, Descr VARCHAR(100),YourXml XML);
INSERT INTO @mockup VALUES
('element exists','<root><element>test</element><SomeOther>blah</SomeOther></root>')
,('element doesn''t exist','<root><SomeOther>blah</SomeOther></root>')
,('element exists, but empty','<root><element/><SomeOther>blah</SomeOther></root>');
--At the end, all should be `<element>new</element>`
UPDATE @mockup SET YourXml.modify('delete (/root/element)[1]');
UPDATE @mockup SET YourXml.modify('insert <element>new</element> as first into (/root)[1]');
SELECT * FROM @mockup;

Answer 2

遵循您的代码结构

SELECT @xml=IDA_Xml,
@isData = IDA_Xml.exist('(/Root/Data[1]/text())[1]')
FROM DATA
WHERE IDA_UId=@guid
If (@xml is NULL)
BEGIN
UPDATE ItemData SET IDA_Xml =  CAST('<root/>' as XML)
WHERE IDA_UId = @guid;
SET @isData = 0;
END 
IF (@isData = 0)
UPDATE ItemData SET IDA_Xml.modify
('
insert <Data Name = "Info">{sql:variable("@number")}</Data>
into (/Root/*)[1]
')
WHERE IDA_UId = @guid;
ELSE
UPDATE ItemData SET IDA_Xml.modify
('
replace value of (/Root/Data[1]/text())[1]
with    sql:variable("@number")
')
WHERE IDA_UId = @guid;

但我最好使用单个更新而不是前两个更新来重组它

SET IDA_Xml =  CAST('construct your entire xml here' as XML)