--各種字符串分函數(shù)

--3.3.1 使用游標(biāo)法進(jìn)行字符串合并處理的示例。
--處理的數(shù)據(jù)
CREATE TABLE tb(col1 varchar(10),col2 int)
INSERT tb SELECT 'a',1
UNION ALL SELECT 'a',2
UNION ALL SELECT 'b',1
UNION ALL SELECT 'b',2
UNION ALL SELECT 'b',3

--合并處理
--定義結(jié)果集表變量
DECLARE @t TABLE(col1 varchar(10),col2 varchar(100))

--定義游標(biāo)并進(jìn)行合并處理
DECLARE tb CURSOR LOCAL
FOR
SELECT col1,col2 FROM tb ORDER BY? col1,col2
DECLARE @col1_old varchar(10),@col1 varchar(10),@col2 int,@s varchar(100)
OPEN tb
FETCH tb INTO @col1,@col2
SELECT @col1_old=@col1,@s=''
WHILE @@FETCH_STATUS=0
BEGIN
?IF @col1=@col1_old
??SELECT @s=@s+','+CAST(@col2 as varchar)
?ELSE
?BEGIN
??INSERT @t VALUES(@col1_old,STUFF(@s,1,1,''))
??SELECT @s=','+CAST(@col2 as varchar),@col1_old=@col1
?END
?FETCH tb INTO @col1,@col2
END
INSERT @t VALUES(@col1_old,STUFF(@s,1,1,''))
CLOSE tb
DEALLOCATE tb
--顯示結(jié)果并刪除測(cè)試數(shù)據(jù)
SELECT * FROM @t
DROP TABLE tb
/*--結(jié)果
col1?????? col2
---------- -----------
a????????? 1,2
b????????? 1,2,3
--*/
GO

/*==============================================*/

--3.3.2 使用用戶定義函數(shù)，配合SELECT處理完成字符串合并處理的示例
--處理的數(shù)據(jù)
CREATE TABLE tb(col1 varchar(10),col2 int)
INSERT tb SELECT 'a',1
UNION ALL SELECT 'a',2
UNION ALL SELECT 'b',1
UNION ALL SELECT 'b',2
UNION ALL SELECT 'b',3
GO

--合并處理函數(shù)
CREATE FUNCTION dbo.f_str(@col1 varchar(10))
RETURNS varchar(100)
AS
BEGIN
?DECLARE @re varchar(100)
?SET @re=''
?SELECT @re=@re+','+CAST(col2 as varchar)
?FROM tb
?WHERE col1=@col1
?RETURN(STUFF(@re,1,1,''))
END
GO

--調(diào)用函數(shù)
SELECT col1,col2=dbo.f_str(col1) FROM tb GROUP BY col1
--刪除測(cè)試
DROP TABLE tb
DROP FUNCTION f_str
/*--結(jié)果
col1?????? col2
---------- -----------
a????????? 1,2
b????????? 1,2,3
--*/
GO

/*==============================================*/

--3.3.3 使用臨時(shí)表實(shí)現(xiàn)字符串合并處理的示例
--處理的數(shù)據(jù)
CREATE TABLE tb(col1 varchar(10),col2 int)
INSERT tb SELECT 'a',1
UNION ALL SELECT 'a',2
UNION ALL SELECT 'b',1
UNION ALL SELECT 'b',2
UNION ALL SELECT 'b',3

--合并處理
SELECT col1,col2=CAST(col2 as varchar(100))
INTO #t FROM tb
ORDER BY col1,col2
DECLARE @col1 varchar(10),@col2 varchar(100)
UPDATE #t SET
?@col2=CASE WHEN @col1=col1 THEN @col2+','+col2 ELSE col2 END,
?@col1=col1,
? col2=@col2
SELECT * FROM #t
/*--更新處理后的臨時(shí)表
col1?????? col2
---------- -------------
a????????? 1
a????????? 1,2
b????????? 1
b????????? 1,2
b????????? 1,2,3
--*/
--得到最終結(jié)果
SELECT col1,col2=MAX(col2) FROM #t GROUP BY col1
/*--結(jié)果
col1?????? col2
---------- -----------
a????????? 1,2
b????????? 1,2,3
--*/
--刪除測(cè)試
DROP TABLE tb,#t
GO

/*==============================================*/

--3.3.4.1 每組 <=2 條記錄的合并
--處理的數(shù)據(jù)
CREATE TABLE tb(col1 varchar(10),col2 int)
INSERT tb SELECT 'a',1
UNION ALL SELECT 'a',2
UNION ALL SELECT 'b',1
UNION ALL SELECT 'b',2
UNION ALL SELECT 'c',3

--合并處理
SELECT col1,
?col2=CAST(MIN(col2) as varchar)
??+CASE
???WHEN COUNT(*)=1 THEN ''
???ELSE ','+CAST(MAX(col2) as varchar)
??END
FROM tb
GROUP BY col1
DROP TABLE tb
/*--結(jié)果
col1?????? col2?????
---------- ----------
a????????? 1,2
b????????? 1,2
c????????? 3
--*/

--3.3.4.2 每組 <=3 條記錄的合并
--處理的數(shù)據(jù)
CREATE TABLE tb(col1 varchar(10),col2 int)
INSERT tb SELECT 'a',1
UNION ALL SELECT 'a',2
UNION ALL SELECT 'b',1
UNION ALL SELECT 'b',2
UNION ALL SELECT 'b',3
UNION ALL SELECT 'c',3

--合并處理
SELECT col1,
?col2=CAST(MIN(col2) as varchar)
??+CASE
???WHEN COUNT(*)=3 THEN ','
????+CAST((SELECT col2 FROM tb WHERE col1=a.col1 AND col2 NOT IN(MAX(a.col2),MIN(a.col2))) as varchar)
???ELSE ''
??END
??+CASE
???WHEN COUNT(*)>=2 THEN ','+CAST(MAX(col2) as varchar)
???ELSE ''
??END
FROM tb a
GROUP BY col1
DROP TABLE tb
/*--結(jié)果
col1?????? col2
---------- ------------
a????????? 1,2
b????????? 1,2,3
c????????? 3
--*/
GO

?

各種字符串合并處理示例.sql