Skip to main content

Creating a network planning using hierarchical queries

Assume we have a table of locations like
Name                                      Null?    Type
----------------------------------------- -------- -----------------
ID NOT NULL NUMBER
NAME NOT NULL VARCHAR2(50)
and a table of possible lines (or route parts) like
Name                                      Null?    Type
----------------------------------------- -------- --------
ID NOT NULL NUMBER
FROM_LOC_ID NOT NULL NUMBER
TO_LOC_ID NOT NULL NUMBER
DISTANCE NOT NULL NUMBER
How can we calculate the best route (in this case: the route with the shortest distance) from a startpoint to an endpoint?
The answer is: By using an hierarchical query:
select dep_name
, arr_name
, route
, distance
, execute(distance) total
from
(
select connect_by_root dep.id dep_id
, connect_by_root dep.name dep_name
, arr.id arr_id
, arr.name arr_name
, level stops
, substr(sys_connect_by_path(dep.name||'-'||arr.name, '->'),3) route
, substr(sys_connect_by_path(lne.id, ','),2) lne_ids
, substr(sys_connect_by_path(lne.distance, '+'),2) distance
from lines lne
, locations dep
, locations arr
where lne.from_loc_id = dep.id
and lne.to_loc_id = arr.id
connect by nocycle prior arr.id = dep.id
)
where dep_name = 'MAASTRICHT'
and arr_name='AMSTERDAM'
ORDER BY 5 ASC
(Remark: The function 'execute' does nothing but returning the result of an execute immediate of a string value).
The outcome of this query is a list of all defined routes from Maastricht to Amsterdam with the shortest route shown first. The
"substr(sys_connect_by_path(dep.name||'-'||arr.name, '->'),3) route"
column returns the route like
"MAASTRICHT-EINDHOVEN->EINDHOVEN-UTRECHT->UTRECHT-AMSTERDAM"
The column
"substr(sys_connect_by_path(lne.distance, '+'),2)"
returns a string that represents the distances to sum:
"86,7+93,6+44,7"
This column is used for calculating the total distance.

So you can use hierarchical queries for a lot more purposes than the obvious who-is-the-manager query.
Ofcourse you won't use this kind of solution to calculate distances (there are far better webservices available for that). In 'real life' we've used this approach (but more elaborated and a lot more difficult) to get the cheapest supplier for the movement of goods from a to b.

Comments

Popular posts from this blog

Refresh selected row(s) in an Interactive Grid

In my previous post I blogged about pushing changed rows from the dabatase into an Interactive Grid. The use case I'll cover right here is probably more common - and therefore more useful!

Until we had the IG, we showed the data in a report (Interactive or Classic). Changes to the data where made by popping up a form page, making changes, saving and refreshing the report upon closing the dialog. Or by clicking an icon / button / link in your report that makes some changes to the data (like changing a status) and ... refresh the report.  That all works fine, but the downsides are: The whole dataset is returned from the server to the client - again and again. And if your pagination size is large, that does lead to more and more network traffic, more interpretation by the browser and more waiting time for the end user.The "current record" might be out of focus after the refresh, especially by larger pagination sizes, as the first rows will be shown. Or (even worse) while you…

Dockerize your APEX development environment

Nowadays Docker is everywhere. It is one of the main components of Continuous Integration / Continuous Development environments. That alone indicates Docker has to be seen more as a Software Delivery Platform than as a replacement of a virtual machine.

However ...

If you are running an Oracle database using Docker on your local machine to develop some APEX application, you will probably not move that container is a whole to test and production environments. Because in that case you would not only deliver a new APEX application to the production environment - which is a good thing - but also overwrite the data in production with the data from your development environment. And that won't make your users very excited.
So in this set up you will be using Docker as a replacement of a Virtual Machine and not as a Delivery Platform.
And that's exactly the way Martin is using it as he described in this recent blog post. It is an ideal way to get up and running with an Oracle database …

apex_application.g_f0x array processing in Oracle 12

If you created your own "updatable reports" or your custom version of tabular forms in Oracle Application Express, you'll end up with a query that looks similar to this one:
then you disable the "Escape special characters" property and the result is an updatable multirecord form.
That was easy, right? But now we need to process the changes in the Ename column when the form is submitted, but only if the checkbox is checked. All the columns are submitted as separated arrays, named apex_application.g_f0x - where the "x" is the value of the "p_idx" parameter you specified in the apex_item calls. So we have apex_application.g_f01, g_f02 and g_f03. But then you discover APEX has the oddity that the "checkbox" array only contains values for the checked rows. Thus if you just check "Jones", the length of g_f02 is 1 and it contains only the empno of Jones - while the other two arrays will contain all (14) rows. So for processing y…