SQL字符串处理问题

[hchen1982]

怎么给某张表的某个字段，判断此字段如果前后无逗号，则前后夹加逗号（，）；如果前后有逗号了或者为null,或者“”则不加
比如：有表A，其中有一个字段users
如果users的值为 ，a，b， 则值不变
如果users 的值为null或者“” 则值也不变
如果users的值为 a,b 则更新为 ,a,b,

[快溜]

select case when user=null or user ='' then user else replace(' '+users+' ',' ',',') end

[hchen1982]

我需要对A表的users字段进行更新到数据库

[快溜]

 update A set users=replace(' '+users+' ',' ',',') where user is not null or user <>''

[gogodiy]

select case when users is null or users ='""' or (left(users,1)=',' and right(users,1)=',') then users
else ','+users+',' end as users from t1

[飘零一叶]

create table tb
(
   users varchar(10)
)
insert into tb
select ',a,b ' union all
select ' ,a,b, ' union all
select 'ab ' union all
select ' a,b' union all
select 'a,b' union all
select '    ' union all
select ' ' union all
select null

UPDATE tb SET users=replace(' '+LTRIM(RTRIM(replace(LTRIM(RTRIM(users)),',',' ')))+' ',' ',',') 
from tb where users is not null and users<>''

SELECT * FROM TB
-----------
users
,a,b,
,a,b,
,ab,
,a,b,
,a,b,
    
 
NULL