Question

我有这个SQL查询

SELECT  r.Address.value('(//City)[1]','VARCHAR(MAX)') "City/@Title" ,   
        (SELECT  r1.FirstName , r1.SecondName 
         FROM Reader r1
         where r.Address.value('(//City)[1]','VARCHAR(MAX)') = r1.Address.value('(//City)[1]','VARCHAR(MAX)')
         FOR XML RAW('Reader'),TYPE) AS "City/Readers"
FROM Reader r
FOR XML PATH(''),ROOT('Cities');

此查询生成此类数据：

<Cities>
  <City Title="New York">
    <Readers>
      <Reader FirstName="JON" SecondName="SHOW" />
      <Reader FirstName="Poll" SecondName="Aeron" />
    </Readers>
  </City>
  <City Title="New York">
    <Readers>
      <Reader FirstName="JON" SecondName="SHOW" />
      <Reader FirstName="Poll" SecondName="Aeron" />
    </Readers>
  </City>
  <City Title="Kharkiv">
    <Readers>
      <Reader FirstName="Slavik" SecondName="Romanov" />
    </Readers>
  </City>
  <City Title="Boca Juniors">
    <Readers>
      <Reader FirstName="Julio " SecondName="Pedro" />
    </Readers>
  </City>
  <City Title="London">
    <Readers>
      <Reader FirstName="Johnny " SecondName="Smith" />
    </Readers>
  </City>
</Cities>

我想删除重复的元素，完全是第二个节点。查询必须生成没有重复项的数据

Answer 1

在构造XML之前选择distinct City会更有效率。这是使用公用表表达式（CTE）的一种可能方式：

;WITH Cities
AS(
    SELECT DISTINCT r.Address.value('(//City)[1]','VARCHAR(MAX)') As City
    FROM Reader r
)

SELECT 
    c.City "City/@Title",
    (SELECT  r1.FirstName , r1.SecondName 
     FROM Reader r1
     where c.City = r1.Address.value('(//City)[1]','VARCHAR(MAX)')
     FOR XML RAW('Reader'),TYPE) AS "City/Readers"
FROM Cities c
FOR XML PATH(''),ROOT('Cities');

<强> Fiddle Demo

如何删除具有特定属性的重复XML数据

1 个答案: