容易自关联表中，查找所有下级数据的函数

if exists (select * from sys.objects where name='func_all_related_levels')    drop function func_all_related_levelsgocreate function func_all_related_levels (    @id int)returns @result table (    id int)asbegin    ------第一次插入数据。    declare @total int;    select @total = count(*) from TestTable where PId = @id    if @total = 0        return;    insert @result        select Id from TestTable where PId = @id;    ------遍历，可用。    declare @cursor int = 0;    while @cursor < @total        begin            declare @nextId int;            select @nextId = id from @result order by id offset (@cursor) rows fetch next 1 rows only;            insert @result                select id from dbo.func_all_related_levels(@nextId);            set @cursor = @cursor + 1;        end    ------游标，出现多余数据。    --declare c cursor for select id from @result;    --open c;    --while @@FETCH_STATUS = 0    --    begin    --        declare @nextId int;    --        fetch next from c into @nextId;    --        insert @result    --            select id from dbo.func_all_related_levels(@nextId);    --    end    --close c;    --deallocate c;    return;end