SQL & PL/SQL

Hi,

I have a problem with a query.

I have a table a with columns x,y,z

I have another table b column with column c. Normally c is the concatenation of x,y,z and that's how these two tables are joined.

Now the problem is that if the contatenation is not fetching values, then I have to compare whether x||y exists.

even if this is not fetching rows, I have to compare x alone and see whether it fetches values and take the corresponding values in table b.

Example

table a

120 20 30 (1)
120 40 50 (2)
120 50 60 (3)
Table
1200000 (1)
1204000 (2)
1202030 (3)

Here row 1 on table a shud pick row 3 on table b
Here row 2 on table a shud pick row 2 on table b
Here row 3 on table a shud pick row 1 on table b

Can anybody help me onb this regard?