Recursive Query for Bill Of Materials

Question

I\'ve just started teaching myself SQL recently and have been able to piece together almost everything I need from various tutorials, but this one has me banging my head aga

Answer 1

I think your logic was basically ok. Here are two improvements. First, the level is incremental so you can see what happens with the recursion. Second, it uses an explicit join:

With BMStudy as (
      select bm.ppn_i, bm.cpn_i, bm.bomname_i, bm.QUANTITY_I, 1 as BOMLevel
      from BM010115 bm
      where bm.PPN_I like '0123105-HWT' and bm.BOMNAME_I like ''
      UNION ALL
      select bb.ppn_i, ba.cpn_i, bb.bomname_i, ba.quantity_i, (BOMLevel + 1) as BOMLevel
      from BMStudy ba join
           BM010115 bb
           on ba.cpn_i = bb.ppn_i
      where bb.BOMNAME_I like ''
     )
select * from BMStudy;

I suspect your problem is the condition where bb.BOMNAME_I like ''. Is it possible that this value is really NULL rather than blank?

You should also check what this non-recursive, one-level down query does:

      select bb.ppn_i, ba.cpn_i, bb.bomname_i, ba.quantity_i, (BOMLevel + 1) as BOMLevel
      from BM010115 ba join
           BM010115 bb
           on ba.cpn_i = bb.ppn_i
      where bb.BOMNAME_I like '' and
            (ba.PPN_I like '0123105-HWT' and ba.BOMNAME_I like '')