Joining two tablew

Question

WITH table1 AS
  SELECT 123 prodid, 111 cid, 'BBB' bid, '563C' fid FROM dual UNION ALL
  SELECT 234 prodid, 222 cid, 'cccc' bid, '663C' fid FROM dual UNION ALL
  SELECT 567 prodid, 22 cid, 'ddd' bid, '763C' fid FROM dual
table2 AS
SELECT NULL cid, 'BBB' bid, NULL fid FROM dual UNION ALL
SELECT 222 cid,  'ccc' bid, '663C' did FROM dual UNION all
SELECT NULL cid, null bid, '563C' fid FROM dual UNION all
SELECT 22 cid, 'BBB' bid, NULL FROM dual
)what i want to do is to join table2 to table1 on the following logic
-- look at cid, if cid is not null then join with cid to table1
-- if cid is null then look at bid and see if it has value. if it does then join wit table2 bid to table1 bid
-- if bid is null, then look at fid and join the two table on fid
so the output should be something like this
prodid    cid      bid    fid
=======  =====     =====   =====
123      null      BBB     NULL
234      222       ccc     663c
123      null      NULL    563c
567      22        BBB     null
can someone help write a query that will join table2 to table1 and product the above output ?
thanks

Answer 1

Hi,
elmasduro wrote:
thanks for the reply but is there a cleaner/easier way than doing the decode in where clause.
i am afraid this can hurt performance as table grows.
if you know a simpler way without using too many decode , please let me know. thanksI'm not sure why you think DECODE won't scale. When you talk about "as table grows", do you mean that you will be adding more and more id columns? If so, then you might find CASE to be cleaner and easier:
SELECT     t1.prodid, t2.cid, t2.bid, t2.fid
FROM     table1     t1
JOIN     table2     t2     ON     CASE
                         WHEN  t2.cid     = t1.cid     THEN  'YES'
                         WHEN  t2.cid     IS NOT NULL     THEN  'NO'
                         WHEN  t2.bid     = t1.bid     THEN  'YES'
                         WHEN  t2.bid     IS NOT NULL     THEN  'NO'
                         WHEN  t2.fid     = t1.fid     THEN  'YES'
                    END = 'YES'
;Dimak showed how to do the job without any DECODE (or CASE). However, UNION is inefficient, and not necessary in this case:
SELECT     t1.prodid, t2.cid, t2.bid, t2.fid
FROM     table1     t1
JOIN     table2     t2     ON     t1.cid     = t2.cid
               OR     (     t2.cid     IS NULL
                    AND     t1.bid     = t2.bid
               OR     (     NVL (t2.bid, t2.cid)     IS NULL
                    AND     t1.fid               = t2.fid
;