sql - 如何将此 SQL 查询重写为分层查询

Question

我有这个计算总重量的 SQL 查询：

select c.componentid, nvl(cs.weightkg, 0) as componentkg,
 (case 
    when exists (select 1 from component where fkcomponentid = c.componentid) then
      (select sum(nvl(cs.weightkg, 0)) as kg FROM  component a, componentstats cs  where a.fkcomponentid is not null and cs.componentstatsid = a.componentstatsid and a.fkcomponentid = c.componentid)
 end) as childrenkg
 from component c, componentstats cs  
 where 
 cs.componentstatsid = c.componentstatsid
 and componentid = ?
 order by c.componentid;

我如何将其重写为分层查询？这可能吗？

编辑：该计划的图片

Answer 1

基本查询将是这样的：

select the_level, c.componentid, NVL( cs.weightkg,0) as componentkg
  from ( select level the_level, componentid from component
           start with componentid = ?
           connect by fkcomponentid = prior componentid
       ) c
  join componentstats using (componentstatsid)
order by the_level, c.componentid

这将为您提供每个单独的组件及其重量。然后，您可以以各种方式进行分组和求和 - 如果您想要原始查询中的子组件权重的总和，则可以按级别进行分组，或者如果您只想要总权重，则可以按所有方式进行分组和求和。