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 table 项目，一列包含 xml 值。我想检查一个字段是否存在并更新它。

我找到了修改现有 xml 值的方法，但是当它为 NULL 时它不起作用

这是我的代码：

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

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次更新来重组它

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

Answer 2

在这种情况下，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;

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