Question

我有以下表格：

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

putput示例（EntryID，TagID）：

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，但是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及其相应的标记逗号分隔列表。

我选择的内容表格如下：

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终选择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

也尝试了这种方式，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

主查询执行group by，因此每个EntryID只能获得一行。

使用相关子查询创建列TagsCommaDelimited。

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

核心化子查询中的连接值', '+T.Name将没有列名，而for xml path('')的空参数将创建没有任何标记的xml。只返回一个文本值。

将type添加到for xml查询时，数据类型将为XML。

要从XML中获取值，您应该使用value()方法。您可以强制转换为字符串，但如果您这样做，那么您将使用&在字符串中获取&。

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()指定您只需要当前元素的值。 [1]告诉SQL Server您希望找到第一个文本节点（此处只有一个），但仍然需要。

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。

value()的第二个参数指定应返回的数据类型。

Answer 2

DECLARE @TableOne TABLE
(
    EntryID INT,
    TagID INT
)

DECLARE @TableTwo TABLE
(
    TagID INT,
    Name NVARCHAR(100)
)

INSERT INTO @TableOne (EntryID,TagID)
VALUES  (1,2)
       ,(1,4)
       ,(1,5)
       ,(2,3)
       ,(2,4)
       ,(2,1)

INSERT INTO @TableTwo (TagID,Name)
VALUES  (1,'Daniel')
       ,(2,'Samuel')
       ,(3,'Petkov')
       ,(4,'Ivan')
       ,(5,'Jack')

/* 
    In this CTE we are going to format the values int the folowing way:

    1   2,4,5
    2   1,3,4

    Or for eaech EntryIDs, we will have all its TagIDs 

*/
;WITH CTE AS
(
    SELECT DISTINCT EntryID
          ,(SELECT SUBSTRING((SELECT ',' + CAST(TagID AS NVARCHAR(10)) FROM @TableOne AS T1 WHERE T1.EntryID=T2.EntryID ORDER BY TagID FOR XML PATH('')),2,200)) AS CSVTags
    FROM @TableOne T2

)
/*
    Here we are replacing the EntryIDs with their names from the @TableTwo:
*/
SELECT EntryID
      ,(SELECT SUBSTRING((SELECT ',' + Name FROM @TableTwo WHERE CSVTags LIKE '%'+CAST(TagID AS NVARCHAR(5))+'%' ORDER BY TagID FOR XML PATH('')),2,200) AS CSV) 
FROM CTE

选择返回按ID分组的逗号分隔列表

2 个答案: