Joining four tables

Question

hi
i have four tables, given the sample data for the relevant field of the tables here under
table company:
company_id     comp_parent_org_id
241     238
457     279
225     200
478     200
10     279
table representative:
rep_id     rep_parent_org_id
238     234
279     170
200     234
table mobile_unit     :     
rep_id     company_id     msisdn     creation_date
238     241     91944400000     1-Sep-08
279     457     91944400005     1-Sep-07
200     225     91944400010     10-Sep-08
200     478     91944400100     5-Jul-08
279     10     91944410100     5-Jul-08
table organization     :
organization_id     name
234     chennai
170     kerala
238     al
279     da
200     sd
now i want to join all these table to get the output as below
table output required: between creation_date in table mobile_unit
name     no of companies     no of msisdns
chennai     3     3
kerala     2     2
the organization table contains the name for all the ids in the table company, representative, etc
name field should reflect the name of the distinct rep_parent_org_id
companies column should count the number of company_id in company table w.r.t comp_parent_org_id (same as rep_id in representative table) which in turn should lie under the rep_parent_org_id
for example here rep_parent_org_id 170 , its name is kerala, then under this id we have got 279 as the rep_id (same as comp_parent_org_id). with 279 as comp_parent_org_id we have got two company_id so no of companies =2
no of msisdns column
rep_parent_org_id 170 , its name is kerala, then under this id we have got 279 as the rep_id. for this 279 rep_id , we have got two msisdn (i.e 91944400005 & 91944410100) so count is 2
i tried in this way as per the answer for my previous question, but am not able to count companies
select DISTINCT o.name, count(mu.msisdn)
FROM RTMS.ORGANIZATION O
INNER JOIN RTMS.REPRESENTATIVE R
     ON O.ORGANIZATION_ID=R.PARENT_ORG_ID
INNER JOIN RTMS.MOBILE_UNIT MU
     ON R.REP_ID=MU.REP_ID
GROUP BY O.NAME
can anybody help me out
thanks
Aemunathan
Edited by: Aemunathan on Sep 10, 2008 11:15 PM

Answer 1

Hi,
Good question! Clear question, carefully written, complete sample data (but not too much), nothing irrelevant, clear sample output.
Would you like to make your questions even better? Enclose the code and data in code tags, as described in the FAQ, to preserve spacing.
You have a one-to-many relationship between representative and mobile_unit, so when you join those two tables, you can multiply rows in representative. For example, there are two rows in mobile_unit with rep_id = 279, so when you join mobile_unit to representative, it looks like there were two rows from representative with rep_id = 279. In the three-table query you posted, that was okay.
You also have a one-to-many relationship between representative and company. If you simply join company the way you joined mobile_unit, those "extra" rows in representative become a problem. For example, there are two rows in company with comp_parent_rep_id = 279. If, because of the join with mobile unit, there seem to be two rows from represnetative with rep_id = 279, then both of the rows from comany will join to both of the rows from representative.
To solve that problem, you should do the join between representative and mobile_unit separately from the join between representative and company. Here's one way to do that:
WITH     m     AS
(     -- Begin sub-query m, counts from mobil_unit
     SELECT     rep_parent_org_id
     ,     COUNT (msisdn)     AS msisdn_cnt
     FROM     representative     r
     JOIN     mobile_unit     mu     ON r.rep_id     = mu.rep_id
     GROUP BY     rep_parent_org_id
)     -- End sub-query m, counts from mobil_unit
,     c     AS
(     -- Begin sub-query c, counts from company
     SELECT     rep_parent_org_id
     ,     COUNT (company_id)     AS company_cnt
     FROM     representative     r
     JOIN     company          c     ON r.rep_id     = c.comp_parent_org_id
     GROUP BY     rep_parent_org_id
)     -- End sub-query c, counts from company
SELECT     o.name
,     m.msisdn_cnt
,     c.company_cnt
FROM     organization     o
JOIN               m     ON o.organization_id     = m.rep_parent_org_id
JOIN               c     ON o.organization_id     = c.rep_parent_org_id
;If there is a chance that some organiztion will have matching rows in mobile_unit but not in company (or vice-versa), then you should make the joins in the main query outer joins.