如何简化嵌套的SQL-Server选择查询

Question

我正在针对包含以下表格的数据库简化一些查询：

1. tShop
2. tShopItems
3. tInvoices
4. tInvoiceRows

有一个嵌套查询生成一个xml输出，如下所示：

 <InvoiceInfo>
  <Invoice Id="100188">Invoice Title</Invoice>
  <InvoiceRows>
    <InvoiceRow Id="80190">Invoice Row 1 Title</InvoiceRow>
    <InvoiceRow>
      <ShopItem Id="20033">Invoice Row 2 Title</ShopItem>
    </InvoiceRow>
  </InvoiceRows>
  <Shop Id="3">Shop Title</Shop>
</InvoiceInfo>

查询是：

SELECT
    (cast(i.InvoiceId as nvarchar)) as 'Invoice/@Id',
    i.InvoiceNote as 'Invoice/text()',
    (SELECT 
        (cast(ir.InvoiceRowId as nvarchar)) as 'InvoiceRow/@Id',
        InvoiceRowNote as 'InvoiceRow/text()',
        (SELECT 
            (cast(si.ShopItemId as nvarchar)) as 'ShopItem/@Id',
            si.ShopItemTitle as 'ShopItem/text()'
        FROM 
            [BizBank.Shops].dbo.tShopItems si
        WHERE
            si.ShopItemId=ir.InvoiceRowItemId
        for 
            xml path(''),root('InvoiceRow'), type
        )
    FROM 
        tInvoiceRows ir
    WHERE
        i.InvoiceId=ir.InvoiceRowInvoiceID
    for 
        xml path(''), root('InvoiceRows'), type
    ),
    (SELECT 
        (cast(s.ShopId as nvarchar)) as 'Shop/@Id',
        s.ShopTitle as 'Shop/text()'
    FROM 
        [BizBank.Shops].dbo.tShops s
    WHERE
        s.ShopID=i.InvoiceShopId
    for 
        xml path(''),type
    )
FROM
    tInvoices i
WHERE
    i.InvoiceID=100188
for 
    XML PATH(''), ROOT('InvoiceInfo'), TYPE

问题是： 有很多嵌套的select语句，如何简化这个查询？