Question

I have three tables in oracle db as newitems, itemdetails, ticketitems table.
Some dummy data as follow:

TICKETITEMS:

id    ticketid     itemid    quantity

1     100          9999      2
2     100          9998      5
3     100          2222      3

ITEMDETAILS:

id    description    col_sumthing   extra_col
9999  Marlboro       val_sumthing   123_op
9998  Cigar Black    val_sumthing   456_pqwe

NEWITEMS:

id    description    col_sumthing
2222  100Pipes       val_different

Initially i had to fetch data only from itemdetails + ticketitems which was very easy using simple joins. Query for which was:

SELECT "TI".*, "I"."ID" AS "ITEMID", "I"."DESCRIPTION", "I"."col_sumthing" 
  FROM "TICKETITEMS" "TI"
 INNER JOIN "ITEMDETAILS" "I" ON TI.ITEMID = I.ID
 WHERE (TI.TICKET = '100')

Something like that.

Now newitem table introduced which may also have some items present in ticketitems table.

So i want a result like:

Final Result:
id    description    itemid    quantity   col_sumthing    extra_col
1     Marlboro       9999      2          val_sumthing    123_op
2     Cigar Black    9998      5          val_sumthing    456_pqwe
3     100Pipes       2222      3          val_different   

The problem I m facing is, it should only check in NEWITEMS when no details found in itemdetails. Any other work around is also welcomed.

Answer 1

You could use two OUTER joins:

SELECT ti.*, 
       nvl(i.id, n.id) itemid, 
       nvl(i.description, n.description) description, 
       nvl(i.col_sumthing, n.col_sumthing) col_sumthing 
  FROM ticketitems ti
  LEFT JOIN itemdetails i ON ti.itemid = i.id
  LEFT JOIN newsitems n ON ti.itemid = n.id
 WHERE ti.ticket = '100'

This will work as long as both detail tables have ID as a primary key. Use COALESCE if you have more than two detail tables.