使用CTE进行字符串拆分的有效方法 [英] Efficient way to string split using CTE
问题描述
我有一张看起来像这样的表
I have a table that looks like
ID Layout
1 hello,world,welcome,to,tsql
2 welcome,to,stackoverflow
所需的输出应该是
Id Splitdata
1 hello
1 world
1 welcome
1 to
1 tsql
2 welcome
2 to
2 stackoverflow
我已经完成了通过下面的查询
I have done this by the below query
Declare @t TABLE(
ID INT IDENTITY PRIMARY KEY,
Layout VARCHAR(MAX)
)
INSERT INTO @t(Layout)
SELECT 'hello,world,welcome,to,tsql' union all
SELECT 'welcome,to,stackoverflow'
--SELECT * FROM @t
;With cte AS(
select F1.id
,O.splitdata
from
(
select *,
cast('<X>'+replace(F.Layout,',','</X><X>')+'</X>' as XML) as xmlfilter
from @t F
)F1
cross apply
(
select fdata.D.value('.','varchar(MAX)') as splitdata
from f1.xmlfilter.nodes('X') as fdata(D)) O
)
select * from cte
但是在性能方面非常糟糕。我正在寻找一种更有效的查询,但仅使用CTE。
But performance wise it is very bad. I am looking for a more efficient query but using CTE only.
推荐答案
您似乎对使用CTE情有独钟,因此请尝试以下操作:
You seem dead set on using a CTE, so try this:
DECLARE @YourTable table (RowID int, Layout varchar(200))
INSERT @YourTable VALUES (1,'hello,world,welcome,to,tsql')
INSERT @YourTable VALUES (2,'welcome,to,stackoverflow')
;WITH SplitSting AS
(
SELECT
RowID,LEFT(Layout,CHARINDEX(',',Layout)-1) AS Part
,RIGHT(Layout,LEN(Layout)-CHARINDEX(',',Layout)) AS Remainder
FROM @YourTable
WHERE Layout IS NOT NULL AND CHARINDEX(',',Layout)>0
UNION ALL
SELECT
RowID,LEFT(Remainder,CHARINDEX(',',Remainder)-1)
,RIGHT(Remainder,LEN(Remainder)-CHARINDEX(',',Remainder))
FROM SplitSting
WHERE Remainder IS NOT NULL AND CHARINDEX(',',Remainder)>0
UNION ALL
SELECT
RowID,Remainder,null
FROM SplitSting
WHERE Remainder IS NOT NULL AND CHARINDEX(',',Remainder)=0
)
SELECT * FROM SplitSting ORDER BY RowID
输出:
RowID Part
----------- -----------------------
1 hello
1 world
1 welcome
1 to
1 tsql
2 welcome
2 to
2 stackoverflow
(8 row(s) affected)
这是一篇有关在SQL Server中拆分字符串的出色文章:当表值参数无法剪切时,SQL Server 2005及更高版本中的数组和列表,作者:Erland Sommarskog
here is an excellent article on splitting strings in SQL Server: "Arrays and Lists in SQL Server 2005 and Beyond, When Table Value Parameters Do Not Cut it" by Erland Sommarskog
编辑,这是另一个版本(但您需要一个数字表) ns与上述结果相同:
EDIT here's another version (but you need a numbers table) returns same results as above:
;WITH SplitValues AS
(
SELECT
RowID,ListValue
FROM (SELECT
RowID, LTRIM(RTRIM(SUBSTRING(List2, number+1, CHARINDEX(',', List2, number+1)-number - 1))) AS ListValue
FROM (
SELECT RowID, ',' + Layout + ',' AS List2
FROM @YourTable
) AS dt
INNER JOIN Numbers n ON n.Number < LEN(dt.List2)
WHERE SUBSTRING(List2, number, 1) = ','
) dt2
WHERE ListValue IS NOT NULL AND ListValue!=''
)
SELECT * FROM SplitValues
在此处查看数字表:创建和填充数字表格的最佳方法是什么?
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