Question

I’m testing SQL query which calculates the total weight of a components. These are the tables structure:

Here I store the key of the parent component and the child component:

-- CREATE TABLES SECTION -------------------------------------------------

-- TABLE COMPONENT

CREATE TABLE COMPONENT(
  COMPONENTID NUMBER NOT NULL,
  FKCOMPONENTID NUMBER,
  COMPONENTSTATSID INTEGER NOT NULL
)
/

-- ADD KEYS FOR TABLE COMPONENT

ALTER TABLE COMPONENT ADD CONSTRAINT COMPONENTID PRIMARY KEY (COMPONENTID)

Here I store the id of the component and the weight:

CREATE TABLE COMPONENTSTATS(
  COMPONENTSTATSID INTEGER NOT NULL,
  COMPONENTTYPEID INTEGER NOT NULL,
  NAME VARCHAR2(200 ) NOT NULL,
  SERIALNUMBER VARCHAR2(150 ),
  WEIGHTKG NUMBER(14,4),
  SIZEWEIGHTMILIM NUMBER(14,4),
)
/

-- ADD KEYS FOR TABLE COMPONENTSTATS

ALTER TABLE COMPONENTSTATS ADD CONSTRAINT COMPONENTSTATSID PRIMARY KEY (COMPONENTSTATSID)
/

I want to create tree with components and using SQL query to calculate the total weight of all components. I made this SQL query:

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;

But for some reason I cannot get the proper result. I only get the first children of the first parent. The goal is to use the COMPONENT table to get the all children and sub children and to calculate the weight.

Can you help me to find where I’m wrong?

Answer 1

You can use a hierarchical query in Oracle to return the tree of components, see http://docs.oracle.com/cd/B19306_01/server.102/b14200/queries003.htm

select componentid,
         (select sum(cs.weightkg)
            from component c2, componentstats cs
           where c2.componentstatsid = cs.componentstatsid
               start with c2.componentid = c1.componentid
         connect by prior c2.componentid = c2.fkcomponentid) sum_weightkg
from component c1
start with c1.fkcomponentid is null
connect by prior componentid = fkcomponentid;

http://www.sqlfiddle.com/#!4/def0e/2