SQL Server performance in xquery with for loop

问题

I have one sql table with xml column, which holds the value like following xml format

<Security xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <Dacl>
    <ACEInformation>
      <UserName>Authenticated Users</UserName>
      <Access>Allow</Access>
      <IsInherited>false</IsInherited>
      <ApplyTo>This object only</ApplyTo>
      <Permission>List Contents</Permission>
      <Permission>Read All Properties</Permission>
      <Permission>Read Permissions</Permission>
    </ACEInformation>
    <ACEInformation>
      <UserName>Local System</UserName>
      <Access>Allow</Access>
      <IsInherited>false</IsInherited>
      <ApplyTo>This object only</ApplyTo>
      <Permission>Read All Properties</Permission>
      <Permission>Read Permissions</Permission>
    </ACEInformation>
  </Dacl>
</Security>

Here, I would like get output from xml column like this

[ Allow -> Authenticated Users -> List Contents; Read All Properties; Read Permissions; -> This object only ]

To achieve this, I am using following for loop query to join values

SELECT  xmlColumn.query('for $item in/Security/Dacl/ACEInformation return("[",data($item/Access)
[1],"->",data($item/UserName)[1],"->", (for $item2 in $item/Permission return concat($item2,";")),"-
>",data($item/ApplyTo)[1],"]")').value('.','NVARCHAR(MAX)')+' ; ' From myTable

The query is working fine, but it takes too much time to give result, for 1000 rows, it is taking 2 mins...can anyone help me to improve performance of this query?.

回答1:

select (
       select '['+
                 A.X.value('(Access/text())[1]', 'nvarchar(max)')+
                 '->'+
                 A.X.value('(UserName/text())[1]', 'nvarchar(max)')+
                 '->'+
                 (
                 select P.X.value('(./text())[1]', 'nvarchar(max)')+';'
                 from A.X.nodes('Permission') as P(X)
                 for xml path(''), type
                 ).value('text()[1]', 'nvarchar(max)')+
                 '->'+
                 A.X.value('(ApplyTo/text())[1]', 'nvarchar(max)')+
               ']'
       from T.xmlColumn.nodes('/Security/Dacl/ACEInformation') as A(X)
       for xml path(''), type
       ).value('text()[1]', 'nvarchar(max)')
from myTable as T

回答2:

Try something like this:

DECLARE @table TABLE (ID INT, XmlCOntent XML)

INSERT INTO @Table VALUES(1, '<Security xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <Dacl>
    <ACEInformation>
      <UserName>Authenticated Users</UserName>
      <Access>Allow</Access>
      <IsInherited>false</IsInherited>
      <ApplyTo>This object only</ApplyTo>
      <Permission>List Contents</Permission>
      <Permission>Read All Properties</Permission>
      <Permission>Read Permissions</Permission>
    </ACEInformation>
    <ACEInformation>
      <UserName>Local System</UserName>
      <Access>Allow</Access>
      <IsInherited>false</IsInherited>
      <ApplyTo>This object only</ApplyTo>
      <Permission>Read All Properties</Permission>
      <Permission>Read Permissions</Permission>
    </ACEInformation>
  </Dacl>
</Security>')

SELECT
    ID,
    Access = XACE.value('(Access)[1]', 'varchar(50)'),
    ApplyTo = XACE.value('(ApplyTo)[1]', 'varchar(50)'),
    AuthUser = XACE.value('(UserName)[1]', 'varchar(50)'),
    Perm1 = XACE.value('(Permission)[1]', 'varchar(50)'),
    Perm2 = XACE.value('(Permission)[2]', 'varchar(50)'),
    Perm3 = XACE.value('(Permission)[3]', 'varchar(50)')
FROM
    @table
CROSS APPLY
    XmlContent.nodes('/Security/Dacl/ACEInformation') AS XTbl(XACE)

Gives me an output of:

来源：https://stackoverflow.com/questions/20161949/sql-server-performance-in-xquery-with-for-loop

标签

sql

sql-server

xquery

xquery-sql