create function GetTown(@name nvarchar(max))
returns nvarchar(max)
begin
declare @i int
set @i=2
          set @name=substring(@name,1,charindex('镇',@name,1))
      while @i<len(@name)
         if substring(reverse(@name),@i,1) like '[0-9]' 
         or substring(reverse(@name),@i,1) like '[a-z]' 
         or substring(reverse(@name),@i,1) = '市'
            return (@name)
         else
            set @name=stuff(...)
...
...
...
end