我被困在一个我无法深入了解的聚合问题上。
我有一些数据最好总结如下
id |phraseId|seqNum|word
=========================
1 |1 |1 |hello
2 |1 |2 |world
3 |2 |1 |black
4 |2 |2 |and
5 |2 |3 |white
我想要一个返回以下数据的查询：
phraseId|completePhrase
========================
1 |hello world
2 |black and white
任何人？
我注意到所有提供的解决方案都使用FOR XML PATH. 这是什么魔法？
尝试这个：
DECLARE @TableA table (RowID int, phraseId varchar(5),seqNum int, word varchar(5))
INSERT INTO @TableA VALUES (1,1,1,'hello')
INSERT INTO @TableA VALUES (2,1,2,'world')
INSERT INTO @TableA VALUES (3,2,1,'black')
INSERT INTO @TableA VALUES (4,2,2,'and')
INSERT INTO @TableA VALUES (5,2,3,'white')
SELECT
c1.phraseId
,STUFF(
(SELECT
' ' + word
FROM @TableA c2
WHERE c2.phraseId=c1.phraseId
ORDER BY c1.phraseId, seqNum
FOR XML PATH('')
)
,1,1, ''
) AS CombinedValue
FROM @TableA c1
GROUP BY c1.phraseId
ORDER BY c1.phraseId
输出：
phraseId CombinedValue
-------- --------------------------
1 hello world
2 black and white
(2 row(s) affected)
一种解决方案是使用FOR XML PATH表达式创建UDF 。
SQL 语句
SELECT PhraseID, dbo.UDF_ConcatWord(PhraseID)
FROM Phrases
GROUP BY PhraseID
创建 UDF
CREATE FUNCTION dbo.UDF_ConcatWord(@phraseID INT) RETURNS VARCHAR(8000) AS
BEGIN
DECLARE @r VARCHAR(8000)
SELECT @r = (
SELECT word + ', '
FROM Phrases
WHERE phraseID = @phraseID
FOR XML PATH('')
)
IF LEN(@r) > 0 SET @r = SUBSTRING(@r, 1, LEN(@r)-1)
RETURN @r
END
GO
在自己修改了一些链接之后，一个更短的解决方案是
SQL 语句
SELECT DISTINCT p1.PhraseID
, STUFF(( SELECT ' ' + p2.word
FROM Phrases AS p2
WHERE p2.PhraseID = p1.PhraseID
FOR XML PATH('')), 1, 1, '') AS completePhrase
FROM Phrases AS p1
ORDER BY p1.PhraseID
我假设您有一个包含每个短语的标题记录的表，这有点作弊。如果缺少，您可以通过从包含以下单词的表中选择不同的短语 ID 列表来构建它：
declare @words table
(id int
,phraseId int
,seqNum int
,word varchar(10)
)
insert @words
select 1,1,1,'hello'
union select 2,1,2,'world'
union select 3,2,1,'black'
union select 4,2,2,'and'
union select 5,2,4,'white'
declare @phrase table
(phraseId int)
insert @phrase
select 1
union select 2
select phraseID
,phraseText AS completePhrase
FROM @phrase AS p
CROSS APPLY (select word + ' ' as [text()]
from @words AS w
where w.phraseID = p.phraseID
for xml path('')
) as phrases (phraseText)
最后我使用了 Lieven 的第二个答案，但发现对于某些字符串组合，该FOR XML PATH('')技巧会导致出现问题：
declare @phrases table
(
id int
,phraseId int
,seqNum int
,word varchar(10)
)
insert
@phrases
values
(1,1,1,'hello'),
(2,1,2,'world'),
(3,2,1,'black'),
(4,2,2,'and'),
(5,2,3,'white')
SELECT
DISTINCT p1.PhraseID,
STUFF(
(
SELECT
' ' + p2.word
FROM
@phrases AS p2
WHERE
p2.PhraseID = p1.PhraseID
FOR XML PATH('')
), 1, 1, '') AS completePhrase
FROM
@phrases AS p1
ORDER BY
p1.PhraseID
工作正常，但如果示例使用在 XML 中使用时需要转义的字符，则会出现问题。例如，通过它运行以下数据：
insert
@words
values
(1,1,1,'hello>'), --notice the less than symbol
(2,1,2,'world'),
(3,2,1,'black')
给
hello> world
并且如果源表被声明为无序，order by则需要an
对原始查询的一个小修改修复了所有问题：
SELECT
DISTINCT p1.PhraseID,
STUFF(
(
SELECT
' ' + p2.word
FROM
@words AS p2
WHERE
p2.PhraseID = p1.PhraseID
ORDER BY
p2.seqNum --required
FOR XML PATH(''),TYPE
).value('.','nvarchar(4000)'),
1,
1,
''
) AS completePhrase
FROM
@words AS p1
ORDER BY
p1.PhraseID