Joining disjoint tables and eliminating repetition

Question

Using customers as an example of my question -- I have 3 tables. Customer with cust_iid, orders with cust_id and preferences with cust_id. I want to see customer id in column 1, customer orders for that customer in column2 and customer preferences for that customer in column 3. Orders and preferences for each customer are not related to each other-only to the customer. When joining on customer id, if Customer John has 2 orders and 1 preference, the preference is repeated for each order. How can I make column 2 and 3 independent of each other so column 2 has each each order once for the customer and column 3 has each preference for the customer listed once? I feel like this should be straightforward to do but cannot find any reference to it. Pointing me where to look would be most appreciated.

Answer 1

Hi,
You'll get better answers faster if you post some sample data (CREATE TABLE and INSERT statements, or a WITH clause, like Pollywog did), and the results you want from that data.
Given the sample data Pollywog psoted, is this the output you want?
   CUST_ID CUST_NM       R_NUM ITEM      PREFERENC
         1 John              1 TV        Blue
         1 John              2 Radio     Green
         1 John              3 Table     Orange
         2 Bob               1 CD Player Purple
         3 Frank             1           LavenderIf so, here's one way to get it:
WITH     union_data   AS
     SELECT     cust_id
     ,     item               AS txt
     ,     ROW_NUMBER () OVER ( PARTITION BY  cust_id
                               ORDER BY          order_no
                       )    AS r_num
     ,     'ORDERS'          AS source_name
     FROM    orders
    UNION
     SELECT     cust_id
     ,     preference_type          AS txt
     ,     ROW_NUMBER () OVER ( PARTITION BY  cust_id
                               ORDER BY          preference_no
                       )    AS p_num
     ,     'PREFERENCES'             AS source_name
     FROM    preferences
SELECT       c.cust_id, c.cust_nm
,       u.r_num     -- You don't have to display this, of course
,       MIN (CASE WHEN u.source_name = 'ORDERS'      THEN txt END)     AS item
,       MIN (CASE WHEN u.source_name = 'PREFERENCES' THEN txt END)     AS preference_type
FROM          customers     c
LEFT OUTER JOIN     union_data     u     ON     u.cust_id     = c.cust_id
GROUP BY  c.cust_id, c.cust_nm
,            u.r_num
ORDER BY  c.cust_id
,            u.r_num
;A customer that had 0 orders and 0 preferences would still appear on the list, but that can be changed if it's not what you want.