SQL to align child values with parent columns

Question

Hi everyone,
I'm stumped on how to develop an sql query that generates a report where my child values are aligned with my parent columns based on matching years.  Here's the example...
create table test_yr (yr_id number primary key, yr_nb number);
insert into test_yr values (1,2013);
insert into test_yr values (2,2014);
insert into test_yr values (3,2015);
create table test_parent (parent_id number primary key, parent_yr_id_begin number, parent_title varchar2(100));
alter table test_parent add foreign key (parent_yr_id_begin) refererences test_yr (yr_id);
insert into test_parent values (1,1,'This rec starts in 2013');
create table test_child (
     child_id number primary key,
     child_parent_id number,
     child_yr_id_begin number,
     child_title varchar2(100),
     child_yr1_val number, child_yr2_val number, child_yr3_val number, child_yr4_val number, child_yr5_val number
alter table test_child add foreign key (child_parent_id) references test_parent (parent_id);
alter table test_child add foreign key (child_yr_id_begin) references test_yr (yr_id);
insert into test_child values (1,1,3,'This rec starts in 2015',10,20,30,40,50);
insert into test_child values (2,1,3,'This rec starts in 2015',15,25,35,45,55);
The child can start at a different begin year than the parent, making yr1 for parent and yr1 for child different.  So for this example, year 1 of the child (2015) = year 3 of the parent.
I can get the values strictly from the child using the following...
select child_yr1_val, child_yr2_val, child_yr3_val, child_yr4_val, child_yr5_val
from test_child
where child_parent_id = 1;
However, I need the report to be based off of the first five years of the parent.  And since the child doesn't start until 2015, the first two years should be zero.  Here is the expected result:
yr1 | yr2 | yr3 | yr4 | yr5
0   | 0   | 10  | 20  | 30
0   | 0   | 15  | 25  | 35
I'm trying to do this using plain sql without having to use pl/sql to derive a dynamic query.  But I need to somehow match up and align the years... such as in this example, yr1(child) = yr3(parent), yr2(child) = yr4(parent), etc.  I'm hoping some joins and case statements will do the trick, but I don't quite know how to utilize them to get the result I need.  Can anyone help?  Oracle 11gR2.
Thanks,
Mark

Answer 1

Hi,
oramark14 wrote:
Hi Frank,
Thanks so much for your reply!  I'll try to digest this solution and implement it this weekend.  I also agree completely about the table design...  I know apps shouldn't drive database design,  ...
If you get indigestion, feel free to ask questions here.
The SELECT ... PIVOT feature isn't very convenient for dealing with missing values.  You may prefer to change the main query like this:
WITH unpivoted_child AS
    SELECT  child_id, child_parent_id
    ,       child_yr_id_begin + child_yr - 1   AS column_num
    ,       val
    FROM    test_child
    UNPIVOT (    val
            FOR  child_yr  IN ( child_yr1_val  AS 1
                              , child_yr2_val  AS 2
                              , child_yr3_val  AS 3
                              , child_yr4_val  AS 4
                              , child_yr5_val  AS 5
    WHERE   child_parent_id  = 1
SELECT    NVL (SUM (CASE WHEN column_num = 1 THEN val END), 0)  AS yr1
,         NVL (SUM (CASE WHEN column_num = 2 THEN val END), 0)  AS yr2
,         NVL (SUM (CASE WHEN column_num = 3 THEN val END), 0)  AS yr3
,         NVL (SUM (CASE WHEN column_num = 4 THEN val END), 0)  AS yr4
,         NVL (SUM (CASE WHEN column_num = 5 THEN val END), 0)  AS yr5
FROM   unpivoted_child
GROUP BY  child_parent_id
,         child_id
ORDER BY  child_parent_id
,         child_id
Also, if you want to see how SELECT ... PIVOT works, this can help show you.
Having 5 separate columns for input can be very conveninet, just like having 5 separate columns for display.  But, as you said, that shouldn't drive the table design.  If necessary, you could create a view that has 5 separate val columns, like your current table, and write an INSTEAD OF trigger for user input.