SQL Server 根据分隔符截取指定位置的子字符串

--截取分隔符之间的字符串
--ChristopherChen 20160804

USE TSQL2012;
IF OBJECT_ID('dbo.StringTest', 'U') IS NOT NULL
	DROP Table dbo.StringTest;
GO

CREATE TABLE dbo.StringTest
(
UserId INT NOT NULL PRIMARY KEY,
NotificationUsers NVARCHAR(4000) NOT NULL
);

INSERT INTO dbo.StringTest VALUES
(7652,'G:q2p9e36a-79f1-4ac7-a869-db70917fa49e:Sherman@earthquake.com');


--法一, 通过游标截取相应的字符串
DROP TABLE #t1;
CREATE TABLE #t1
(
UserId INT NOT NULL,
NotificationUsers NVARCHAR(4000) NOT NULL
);

DECLARE @UserId INT, @NotificationUser VARCHAR(4000),@NewList VARCHAR(4000);
DECLARE N_Cursor CURSOR FOR
SELECT UserId, NotificationUsers
FROM dbo.StringTest

OPEN N_Cursor
FETCH NEXT FROM N_Cursor INTO @UserId, @NotificationUser
       WHILE @@FETCH_STATUS =0
       BEGIN
       SET @Newlist = '';
              WHILE CHARINDEX('|',@NotificationUser)>0
              BEGIN
              SET @NewList = @NewList + stuff(LEFT(@NotificationUser,CHARINDEX('|',@NotificationUser)-1),1, 39,'') + ','
              SET @NotificationUser=STUFF(@NotificationUser,1,CHARINDEX('|',@NotificationUser),'')
              END
       SET @NewList = @NewList + stuff(@NotificationUser,1,39,'')
       INSERT #t1 VALUES(@UserId, @NewList)
       FETCH NEXT FROM N_Cursor INTO @UserId, @NotificationUser
       END
CLOSE N_Cursor;
DEALLOCATE N_Cursor;

SELECT UserId,NotificationUsers FROM #t1;

DROP TABLE #t1;

--法二, 通过PARSENAME()函数截取指定位置的字符
--需要注意的是PARSENAME()原本是为截取四段式Server连接串或IP设计的，仅支持四段内的以'.'作分隔符的字符串;另外PARSENAME函数分段参数依据倒序排列
SELECT UserId
--截取中间部分
,REPLACE(PARSENAME(REPLACE(REPLACE(NotificationUsers,'.','&'),':','.'),2),'&','.') Id
--截取末端部分
,REPLACE(PARSENAME(REPLACE(REPLACE(NotificationUsers,'.','&'),':','.'),1),'&','.') Email
FROM dbo.StringTest

--法三, charindex与substring函数组合截取字符
--注意表达式charindex(':',NotificationUsers,charindex(':',NotificationUsers)+1)实际取得的是第二个':'的索引值
SELECT NotificationUsers
--截取中间部分
,substring(NotificationUsers,charindex(':',NotificationUsers)+1,case when charindex(':',NotificationUsers)=0 then len(NotificationUsers) else charindex(':',NotificationUsers,charindex(':',NotificationUsers)+1)-charindex(':',NotificationUsers)-1 end) Id
--截取末端部分
,right(NotificationUsers,len(NotificationUsers)-charindex(':',NotificationUsers,charindex(':',NotificationUsers)+1)) Email
FROM dbo.StringTest 

--法四, 解析XML
WITH CTE AS (
SELECT UserId,NotificationUsers,convert(xml,'<s>'+replace(NotificationUsers,':','</s><s>')+'</s>') NotificationUsersXML from dbo.StringTest
)
SELECT *
--截取中间部分
,NotificationUsersXML.value('(/s)[2]','nvarchar(max)') Id
--截取末端部分
,NotificationUsersXML.value('(/s)[3]','nvarchar(max)') Email
FROM CTE