create table tb(col varchar(100))
insert into tb values('5612@朱岚;')
insert into tb values('5708@王洁琪;5117@刘桂珍;')
insert into tb values('5594@徐婷;5708@王洁琪;5426@谢静佳;5091@刘照晶;')
go

create function dbo.f_str(@col varchar(100)) returns varchar(100)
as
begin
  declare @str varchar(100)
  declare @i as int
  declare @j as int
  set @str = ''
  set @i = 1
  set @j = len(@col) - len(replace(@col , ';' , ''))
  while @i <= @j
  begin
    set @str = @str + substring(@col , charindex('@',@col) + 1 , charindex(';',@col) -  charindex('@',@col) )
    set @col = substring(@col , charindex(';',@col) + 1 , len(@col))
    set @i = @i + 1
  end
  return @str
end
go

--调用函数
select newcol = dbo.f_str(col) from tb

drop function dbo.f_str
drop table tb

/*
newcol                   
-------------------------
朱岚;
王洁琪;刘桂珍;
徐婷;王洁琪;谢静佳;刘照晶;

（所影响的行数为 3 行）
*/