RetrieveTreeHierarchy / SQL server / SQL/T-SQL

General way to handle trees. Fails when the sequence varchar length is exceeded - in this case 100 levels.
Author Nigel Rivett

-- create test data
create table #z (id int, name varchar(20), Parent int null)
insert #z select   1,  'foo', null
insert #z select     2,  'foo2',   null
insert #z select     3,  'foo2a',      2
insert #z select    11,  'foo2aa',     3
insert #z select    12,  'foo2aaa',   11
insert #z select    13,  'foo2ab',     3
insert #z select    14,  'foo2ac',     3
insert #z select     4,  'foo2b',      2
insert #z select     5,  'foo3',   null
insert #z select     6,  'foo3b',      5
insert #z select     7,  'foo3ba',     6
insert #z select     8,  'foo4',   null
insert #z select     9,  'fooa',       1
insert #z select    10,  'foo2ba',     4

-- Get the hierarchy
create table #tree (id int, sequence varchar(1000), levelNo int)
-- insert top level (to get sub tree just insert relevent id here)
insert #tree select id, right(space(10) + convert(varchar(10),id),10), 1 from #z where Parent is null
declare @i int
select @i = 0
-- keep going until no more rows added
while @@rowcount > 0
begin
     select @i = @i + 1
     insert #tree
     -- Get all children of previous level
     select #z.id, sequence + right(space(10) + convert(varchar(10),#z.id),10), @i + 1
     from #z, #tree 
     where #tree.levelNo = @i
     and #z.Parent = #tree.id
end

-- output with hierarchy formatted
select space((levelNo-1)*4) + #z.name 
from #tree, #z 
where #tree.id = #z.id
order by sequence

drop table #tree
drop table #z

/*  OUTPUT
foo
    fooa
foo2
    foo2a
        foo2aa
            foo2aaa
        foo2ab
        foo2ac
    foo2b
        foo2ba
foo3
    foo3b
        foo3ba
foo4
*/