create table tb
(
   a varchar(5),
   b varchar(10),
   c varchar(10),
   d varchar(10)
)
insert into tb
select 'a,a','tt,tt','cc,dd','ee,ee' union all
select 'b,b','tt,cc','cc,cc','ff,gg' union all
select 'c,c','aa,bb','tt,tt','aa,aa'

select case when LEFT(a,CHARINDEX(',',a)-1)=right(a,len(a)-CHARINDEX(',',a)) then LEFT(a,CHARINDEX(',',a)-1) else a end as a
, case when LEFT(b,CHARINDEX(',',b)-1)=right(b,len(b)-CHARINDEX(',',b)) then LEFT(b,CHARINDEX(',',b)-1) else b end as b
, case when LEFT(c,CHARINDEX(',',c)-1)=right(c,len(c)-CHARINDEX(',',a)) then LEFT(c,CHARINDEX(',',c)-1) else c end as c
, case when LEFT(d,CHARINDEX(',',d)-1)=right(d,len(d)-CHARINDEX(',',d)) then LEFT(d,CHARINDEX(',',d)-1) else d end as d
from tb

---------------
a    b    c    d
a    tt    cc,dd    ee
b    tt,cc    cc,cc    ff,gg
c    aa,bb    tt,tt    aa

------解决方案--------------------
Assembly code
create table #temp
(
    a varchar(100),
    b varchar(100),
    c varchar(100),
    d varchar(100)
)
insert into #temp
select 'a,a', 'tt,tt', 'cc,dd', 'ee,ee' union all
select 'b,b', 'tt,cc', 'cc,cc', 'ff,gg' union all
select 'c,c', 'aa,bb', 'tt,tt', 'aa,aa' 
select * from #temp

SELECT 
    a = CASE WHEN (SUBSTRING(a, 1, CHARINDEX(',', a)-1)) = (SUBSTRING(a, CHARINDEX(',', a)+1, LEN(a)-CHARINDEX(',', a))) THEN (SUBSTRING(a, 1, CHARINDEX(',', a)-1)) ELSE a END,
    b = CASE WHEN (SUBSTRING(b, 1, CHARINDEX(',', b)-1)) = (SUBSTRING(b, CHARINDEX(',', b)+1, LEN(b)-CHARINDEX(',', b))) THEN (SUBSTRING(b, 1, CHARINDEX(',', b)-1)) ELSE b END,
    c = CASE WHEN (SUBSTRING(c, 1, CHARINDEX(',', c)-1)) = (SUBSTRING(c, CHARINDEX(',', c)+1, LEN(c)-CHARINDEX(',', c))) THEN (SUBSTRING(c, 1, CHARINDEX(',', c)-1)) ELSE c END,
    d = CASE WHEN (SUBSTRING(d, 1, CHARINDEX(',', d)-1)) = (SUBSTRING(d, CHARINDEX(',', d)+1, LEN(d)-CHARINDEX(',', d))) THEN (SUBSTRING(d, 1, CHARINDEX(',', d)-1)) ELSE d END
FROM #temp

------解决方案--------------------
更新：
Assembly code
insert into #temp
select 'a', 'tt,tt', 'cc,dd', 'ee,ee' union all
select 'b', 'tt,cc', 'cc,cc', 'ff,gg' union all
select 'c', 'aa,bb', 'tt,tt', 'aa,aa' 
select * from #temp

SELECT 
    a = CASE WHEN (LEN(a)%2 = 1 AND (CHARINDEX(',', a) = (LEN(a)+1)/2) AND LEFT(a, (LEN(a)-1)/2) = RIGHT(a, (LEN(a)-1)/2)) THEN LEFT(a, (LEN(a)-1)/2) ELSE a END,
    b = CASE WHEN (LEN(b)%2 = 1 AND (CHARINDEX(',', b) = (LEN(b)+1)/2) AND LEFT(b, (LEN(b)-1)/2) = RIGHT(b, (LEN(b)-1)/2)) THEN LEFT(b, (LEN(b)-1)/2) ELSE b END,
    c = CASE WHEN (LEN(c)%2 = 1 AND (CHARINDEX(',', c) = (LEN(c)+1)/2) AND LEFT(c, (LEN(c)-1)/2) = RIGHT(c, (LEN(c)-1)/2)) THEN LEFT(c, (LEN(c)-1)/2) ELSE c END,
    d = CASE WHEN (LEN(d)%2 = 1 AND (CHARINDEX(',', d) = (LEN(d)+1)/2) AND LEFT(d, (LEN(d)-1)/2) = RIGHT(d, (LEN(d)-1)/2)) THEN LEFT(d, (LEN(d)-1)/2) ELSE d END
FROM #temp

------解决方案--------------------
用函数吧
SQL code
if object_id('[tb]') is not null drop table [tb]
go
create table [tb]([a] varchar(5),[b] varchar(8),[c] varchar(8),[d] varchar(8))
insert [tb]
select 'a,a','tt,tt','cc,dd','ee,ee' union all
select 'b,b','tt,cc','cc,cc','ff,gg' union all
select 'c','d','a','a' union all
select 'c,c','aa,bb','tt,tt','aa,aa' union all
select 'c','a','d','b' union all
select 'c,c,c','aa,bb,cc','tt,tt,tt','aa,aa,aa'
go

create function f_test(@s varchar(100))
returns varchar(200)
as
begin
  declare @rel varchar(200);
  declare @t table(a varchar(100));
  set @s=@s+','
  while charindex(',',@s)>0
  begin
    inse