Help needed in retrieving parent child relationship values

Question

Hi,
I have a requirement to get parent child relationship values as below.
Ex: Address table
cont cont_code state state_code
C1 10 S1 1
C1 10 S2 2
C1 10 S3 3
C2 20 S4 4
C2 20 S5 5
C3 30 S6 6
C3 30 S7 7
C3 30 S8 8
I want a result of country/state and corresponding code like below.
corresponding states should be displayed under each country with some space appended to it.
Geography code
C1 10
S1 1
S2 2
S3 3
C2 20
S4 4
S5 5
C3 30
S6 6
S7 7
S8 8
I am using oracle 10g version.
Thanks in advance.

Answer 1

Hi,
When you post formatted text (like your output) on this site, type these 6 characters:
\(small letters only, inside curly brackets) before and after each section of formatted text, to preserve spacing.
I think you're saying that you want this output:GEOGRAPHY CODE
C1 10
S1 1
S2 2
S3 3
C2 20
S4 4
S5 5
C3 30
S6 6
S7 7
S8 8
If so, UNION, as Hoek suggested, is a good way.
GROUP BY ROLLUP is more efficient, but harder to understand:SELECT     CASE
          WHEN GROUPING (state) = 1
          THEN cont
          ELSE ' ' || state
     END          AS geography
,      CASE
          WHEN GROUPING (state) = 1
          THEN MAX (cont_code)
          ELSE MAX (state_code)
     END          AS code
FROM     t
GROUP BY cont
,      ROLLUP (state)
ORDER BY cont
,      state          NULLS FIRST
By the way, this looks like a bad table design.
In a relational database, the fact that the name 'C1' belongs to cont_code 10 should only be stored in one place.  You have the same information on 3 separate rows.
Also, if 'C1' and 'S1' are both names, they should probably be in the same column, so that (to give just one example) you can find the information about 'x1' without knowing if it is a cont or a state.
A better design would be.NAME     CODE     PARENT     DSCR
====     ====     ======     ====
C1     10          CONT
S1     1     10     STATE
S2     2     10     STATE
S3     3     10     STATE
C2     20          CONT
S4     4     20     STATE
S5     5     20     STATE
C3     30          CONT
S6     6     30     STATE
S7     7     30     STATE
S8     8     30     STATE
If the data is this simple, then the dscr column isn't needed.  Whether parent is NULL or not tells whether the rows represents a cont or a state.
To get the results you want from a table like this, you could use CONNECT BY.  Using either UNION or ROLLUP, you have to know, at the time you write the query, how many levels there will be in the parent-child tree, and the length of the code is proportional to that depth, and the table has to be changed if you ever need to add another level.  CONNECT BY can handle any number of levels, and the length and complexity of the code is the same whether you have just 2 levels (countries and strates), or 7 levels (continents, regions, countiries, states, districts, cities and neighborhoods) or 72 levels.  The table doesn't need any more columns, no matter how deep the tree gets.
Edited by: Frank Kulash on Sep 16, 2010 11:54 AM