SQL Server中几种特殊的“字符串到列表”的处理函数 |
| 6/17/2008 12:05:12 AM |
普通的字符串分割函数已经见得很多了，写法性能也大不一样，通常都是直接基于字符串的处理，这里就不列出了。下面介绍几种特殊的方式
1.使用xml
性能应该不如字符串处理快，没有具体测试过
 IF OBJECT_ID('dbo.Split') IS NOT NULL
DROP FUNCTION dbo.Split
GO
CREATE FUNCTION dbo.Split(@data NVARCHAR(MAX), @delimiter NVARCHAR(5))
RETURNS @t TABLE (data NVARCHAR(max))
AS
BEGIN
DECLARE @textXML XML;
SELECT @textXML = CAST('<d>' + REPLACE(@data, @delimiter, '</d><d>') + '</d>' AS XML);
INSERT INTO @t(data)
SELECT T.split.value('.', 'nvarchar(max)') AS data
FROM @textXML.nodes('/d') T(split)
RETURN
END
GO
DECLARE @text NVARCHAR(max)
SELECT @text = REPLICATE('ab,', 300) + 'ab'
SELECT * FROM dbo.Split(@text, ',')
2. 用xml作为参数
  /**//* Assumes XML is as such
 <list>
<i>1</i>
<i>23</i>
</list>
etc
Uses minimal xml markup to keep input size as small as possible
 */
ALTER FUNCTION dbo.fnXml2IntList(@xmlList xml)
RETURNS TABLE
AS
RETURN (SELECT tList.ListValue.value('.', 'int') AS ListValue
FROM @xmlList.nodes('list/i') AS tList(ListValue))
GO
使用示例：
SELECT * FROM dbo.fnXml2IntList
( '<list>
<i>1</i>
<i>23</i>
</list>'
)
3.利用笛卡尔集的方式
-- =============================================
-- Author: 代码乱了(靳如坦)
-- Create date: 2008-06-10
-- Description: 把以','分隔的字符串，转换成table
-- 示例 :select * from [dbo].[SpliteStringToList]('123,xxx,dfdsf,rer')
-- =============================================
create Function [dbo].[SpliteStringToList](@strings varchar(2000))
Returns @ReturnTable Table(ID varchar(max))
As
Begin
Insert @ReturnTable
select substring(c,2,charindex(',',c,2)-2) as empno from
(
select substring(csv.emps,iter.pos,len(csv.emps)) as c from
(
select ','+@strings+',' as emps
) csv,
(
--select id as pos from t100
--生产1-10000的结果集
Select a + b * 10 +c*100+d*1000+1 as pos From
(Select 0 As a Union Select 1 Union Select 2 Union Select 3 Union Select 4 Union Select 5 Union Select 6 Union Select 7 Union Select 8 Union Select 9 ) A,
(Select 0 As b Union Select 1 Union Select 2 Union Select 3 Union Select 4 Union Select 5 Union Select 6 Union Select 7 Union Select 8 Union Select 9 ) B,
(Select 0 As c Union Select 1 Union Select 2 Union Select 3 Union Select 4 Union Select 5 Union Select 6 Union Select 7 Union Select 8 Union Select 9 ) c,
(Select 0 As d Union Select 1 Union Select 2 Union Select 3 Union Select 4 Union Select 5 Union Select 6 Union Select 7 Union Select 8 Union Select 9 ) d
) iter where iter.pos <= len(csv.emps)
)x
where len(c) > 1 and substring(c,1,1) = ','
Return
End
该函数主要运用了笛卡尔集的特点，速度上稍微慢于普通字符串处理，不过比较稳定，没有循环处理，结构上比较清晰。
需要注意到是，这个函数只能处理数组大小为10000的字符串，如果想处理更多。建议把上面的产生1-10000的结果集再扩大，并放在一个表内，这样性能肯定会有所提高，我这儿只是为了方便直接用内嵌视图，实际应用中应该先生成1-10000（根据实际应用可大可小）的数据表。如果大家发现什么问题，欢迎指正，谢谢。
4.运用WITH AS，递归
待续。。。。 |
|
| 作者：代码乱了
来源：博客园 |