选择返回按ID分组的逗号分隔列表

Question

我有以下表格:

EntryTag
---------
EntryID
TagID

putput示例(EntryID,TagID):

1 2
1 4
1 5
2 3
2 4
2 5
etc...

和

Tags
----
TagID
Name

示例输出:

1 peas
2 corn
3 carrots
...etc.

我希望每个条目带回标签列表,但作为标记以逗号分隔的一行.

例如,我想看到这个:

EntryID     TagsCommaDelimited
-------     ------------------
1           corn, peas, carrots
2           barley, oats
...and so on 

所以我需要列出每个EntryID及其对应的标记逗号分隔列表.

我选择的内容表如下所示:

Content
--------
ID   -(which is in essence the EntryID, they didn't make it consistent)
Description
..etc.

这是我尝试过的,但我的语法没有运气:

declare @tagsCommaDelimited varchar (200) 
set @tagsCommaDelimited = '';


With AllEntryTags_CTE(Name, EntryID )
as
(
    select Tags .Name,
           entryTags.EntryID 
    from  EntryTag entryTags
    join Tags on tags.Id = entryTags.TagID
    group by entryTags.EntryID, tags.Name, entryTags.TagID 
),

TagsByEntryCommaDelimited_CTE( EntryID, CommaDelimitedTags)
as
(
    select  distinct allTags.EntryID,
            (select @tagsCommaDelimited from ( select @tagsCommaDelimited = coalesce (case when @tagsCommaDelimited = '' then allTags.Name
                                                                                      else @tagsCommaDelimited + ',' + allTags.Name end ,'') as CommaDelimitedTags
    from  AllEntryTags_CTE allTags  
)

select EntryID, CommaDelimitedTags from TagsByEntryCommaDelimited_CTE

--------------------------- UPDATE ---------------------- ------------

现在我和gotgn一起去测试了

我现在遇到的问题是,我正在尝试在我的最后一个select语句中使用最后一个CTE来获取标记名称的逗号分隔列表.但是它说我的语法不正确:

;WITH CommaDelimitedTagIDs AS
(
    SELECT DISTINCT EntryID,
    (SELECT SUBSTRING((SELECT ',' + CAST(TagID AS NVARCHAR(10)) 
                       FROM EntryTag AS T1 WHERE T1.EntryID=T2.EntryID 
                       ORDER BY TagID 
                       FOR XML PATH('')),2,200)) AS commaDelimitedTagIDs
    FROM EntryTag T2 
),

CommaDelimittedTagNames_CTE (EntryID, CommaDelimitedTagNames) as
( 
    SELECT EntryID, (SELECT SUBSTRING((SELECT ',' + Name 
                     FROM Tags 
                     WHERE commaDelimitedTagIDs LIKE '%'+CAST(ID AS NVARCHAR(5))+'%'  
                     ORDER BY ID FOR XML PATH('')),2,200) AS CSV) 
    FROM CommaDelimitedTagIDs
)

--select EntryID, CommaDelimitedTagNames from CommaDelimittedTagNames_CTE


SELECT  Title,
        [Description],
        DateSyndicated,
        DateUpdated,
        1, 
        CAST([Text] AS NVARCHAR(MAX)),
        Author,
        (select CommaDelimitedTagNames from CommaDelimittedTagNames_CTE) as tagNamesCommaDelimited 
 FROM Content
 Join CommaDelimittedTagNames_CTE tags on tags.EntryID = Content.ID
 group by ID, Title, [Description], 
          DateSyndicated, DateUpdated, 
          CAST(subtextContent.[Text] AS NVARCHAR(MAX)), Author 

也试过这种方式,没有运气

  Select
    ....other fields
    (select CommaDelimitedTagNames from CommaDelimittedTagNames_CTE tagNames 
     join subContent on subContent.ID = tagNames.EntryID) as tags 
  FROM Content as subContent

好吧我猜你不能加入,我不得不把它改成Where.不知道为什么,但这现在有效:

   Select
    ....other fields
    (select CommaDelimitedTagNames from CommaDelimittedTagNames_CTE tagNames 
     where Content.ID = tagNames.EntryID) as tags 
  FROM Content 

Answer 1

select ET1.EntryID,
       (
       select ', '+T.Name
       from Tags as T
         inner join EntryTag as ET2
           on T.TagID = ET2.TagID
       where ET1.EntryID = ET2.EntryID
       for xml path(''), type
       ).value('substring(text()[1], 3)', 'varchar(max)') as TagsCommaDelimited
from EntryTag as ET1
group by ET1.EntryID

解析查询

主查询会执行一次操作,group by因此每个查询只能获得一行EntryID.

该列TagsCommaDelimited使用相关子查询创建.

在SQL Server for xml path中用于创建查询结果的XML表示.通过使用列别名和参数path和,您可以很好地控制XML的创建方式root.

核心', '+T.Name化子查询中的连接值将没有列名和空参数来for xml path('')创建没有任何标记的xml.将只返回一个文本值.

添加type到for xml查询时,数据类型将是XML.

要从XML中获取值,您应该使用该value()方法.您可以强制转换为字符串,但如果您这样做,您可以&在任何地方使用字符串&.

value()函数中的第一个参数是用于获取所需值的xQuery表达式.使用text()指定你只想为当前元素的值.[1]告诉SQL Server你想要找到第一个文本节点(你这里只有一个),但它仍然是必要的.

for xml查询创建的字符串在字符串的开头有一个额外的逗号和一个空格,需要删除.在这里,我使用XQuery函数substring来获取除前两个字符之外的所有内容.

第二个参数,用于value()指定应返回的数据类型.