有效地从 xml 中删除节点

Question

这是一个挑战。下面的代码显示了从 xml 变量中删除一些行的工作方法。目的是删除没有将 primaryKey 属性设置为 1 的行，其中 oldValue 和 newValue 属性相同。（我的意思是，两者都可以为空或都具有相同的值）下面的代码演示了这种情况。但是，下面的代码使用了游标。如果可以使用单个 @xml.modify 或至少不必诉诸于使用游标来执行删除，我不会感到惊讶。

declare @xml xml ='<changes schemaName="Security" tableName="AccessProfiles">
  <column name="AccessProfileId" primaryKey="1" oldValue="114" newValue="114" />
  <column name="AccessProfileName" oldValue="test" newValue="Testing" />
  <column name="DeleteMeSame" oldValue="testValue" newValue="testValue" />
  <column name="DeleteMeNull" />
  <column name="KeepMePrimaryNull" primaryKey="1" />
  <column name="KeepMePrimarySame" primaryKey="1" oldValue="sameValue" newValue="sameValue"/>
</changes>';

declare @columnName sysname;

declare deleteNodesCursor cursor fast_forward for
    with shreddedXml as (
        select
            N.value( '@name' , 'sysname' ) as name,
            N.value( '@primaryKey' , 'bit' ) as primaryKey,
            N.value( '@oldValue' , 'varchar(max)' ) as oldValue,
            N.value( '@newValue' , 'varchar(max)' ) as newValue
        from @xml.nodes('/changes/column') as T(N)
    )
    select
        Name
    from shreddedXml
    where primaryKey is null
    and (oldValue = newValue
    or  (oldValue is null and newValue is null))

open deleteNodesCursor

while (1=1)
begin
    fetch next from deleteNodesCursor into @columnName
    if @@fetch_status != 0
        break;

    set @xml.modify( 'delete /changes[1]/column[@name= sql:variable("@columnName")]' )
end;

close deleteNodesCursor;
deallocate deleteNodesCursor;

select @xml

总而言之，问题是，我怎样才能有效地完成这项工作？

Answer 1

"The intention is to delete the rows which do not have the primaryKey attribute set to 1, where the oldValue and newValue attributes are the same. (by the same I mean, both can be null or both having the same value)"

可以将其翻译成单个 @xml.modify 表达式，如下所示（在 SQL Server 2008R2 中测试和工作）：

set @xml.modify('delete /changes/column[not(@primaryKey=1) and not(@oldValue!=@newValue)]')

有效地从 xml 中删除节点

delete nodes from xml efficiently

xml

tsql

xpath

xml.modify