I need a logic immediately

Question

There are four tables for me
Table_A TAble_B TAble_C TAble_D
Table_A
ID number
mn_nbr Varchar(8)
Table_B
ID number
sec_NBR varchar(3)
Table_C
MN_NBR VArchar(8)
SEC_NBR VArchar(3)
m_mn_nbr Varchar(11)
m_sec_nbr VArchar(3)
Table_D
m_mn_nbr VArchar(11)
m_sec_nbr VArchar(3)
extn varchar(4)
For every record from TAble_A and TAble_B
we have to find record in TAble_C and pickup m_mn_nbr,m_sec_nbr
If we find it is fine else we will expand mn_nbr to be like m_mn_nbr by appending 000
then with m_mn_nbr and m_sec_nbr we have to find a record from table_d
if it is not found then we have to check with m_mn_nbr and m_sec_nb = 'XXX'
else the value of EXTN will be '0000'.
Please can some one help me in gettin this logic.
Thanks

Answer 1

Like currently I am dealing with the first three tables
And the rows I had inserted as follows
Table A
ID --- mn_nbr
1111 11112222
2222 22221111
3333 33332222
Table B
ID --- sec_nbr
1111 031
2222 041
3333 021
Table C
mn_nbr -- sec_nbr m_mn_nbr m__sec_nbr
11112222 031 10111112222 031
So with my query I am able to pick up the record from Table C
Query is as follows
select a.MN_NBR,a.SEC_NBR,a.m_mn_nbr ,a.m_sec_nbr
from table_C A,TABLE_A B,TABLE_B C
where B.Id = C.ID
and A.MN_NBR= B.MN_NBR
and A.SEC_NBR= C.SEC_NBR
But there are no records corresponding to 2nd and 3rd rows of Table A and Table B
As the data will not be found I need to expand myself and pick it up
when evver record is not found I want to get m_mn_clm_nbr as mn_nbr||'000'
This one I am not getting.
Now combinedly I need to pick up three records from TAble_C
One record is existing and the other two as expanded records
THanks