Sql 查询父子记录

Question

I need to find out final parent record for each child with a recursive logic until I find parent as null eg child=12 has final parent equal to 7. So as we traverse to find final parent all the non null values for L1, L2 and L3 will be populated in child record. May I get some guidance what SQL function I should use to generate following output.

Input:

Child Parent  L1   L2   L3
12    435     xyz
435    7      xyz  abc  def
7     Null    xyz

Output:

 Child    L1   L2   L3
     7     xyz 
     435   xyz  abc  def
     12    xyz  abc  def

Create Table Statement:

CREATE TABLE mytable(
    child NUMBER,
    parent NUMBER,
    l1 varchar2(3),
    l2 varchar2(3),
    l3 varchar2(3)
);

populate data script:

insert into mytable(child, parent, l1, l2, l3)
values (12, 435, 'xyz', null, null);
insert into mytable(child, parent, l1, l2, l3)
values (435, 7, 'xyz', 'abc', 'def');
insert into mytable(child, parent, l1, l2, l3)
values (7, null, 'xyz', null, null);

Answer 1

I think you want to use the connect by to get the proper order. You can get the last non null value by using the last value ignore nulls clause.

  SELECT child, parent,
 last_value(l1) ignore nulls over (
           order by level rows between unbounded preceding and current row
         ) l1,
 last_value(l2) ignore nulls over (
           order by level rows between unbounded preceding and current row
         ) l2,
 last_value(l3) ignore nulls over (
           order by level rows between unbounded preceding and current row
         ) l3
      FROM mytable
      START WITH child = 7
      CONNECT BY PRIOR child = parent

here is the fiddle http://sqlfiddle.com/#!4/b36736/10

Answer 2

You could also try below sql. It will work for many cases.

with cte (CHILD, PARENT, L1, L2, L3,  temp_L1, temp_L2, temp_L3) as (
  select CHILD, PARENT, L1, L2, L3
        , L1 temp_L1, L2 temp_L2, L3 temp_L3
  from mytable
  where mytable.parent is null
  union all
  select t.CHILD, t.PARENT, t.L1, t.L2, t.L3
        , nvl2(t.L1, t.L1, c.temp_L1)temp_L1
        , nvl2(t.L2, t.L2, c.temp_L2)temp_L2
        , nvl2(t.L3, t.L3, c.temp_L3)temp_L3
  from mytable t 
  join cte c on t.parent = c.child
)
search depth first by child set order1
select CHILD, /*PARENT,*/ temp_L1 L1, temp_L2 L2, temp_L3 L3
from cte
order by order1
;