SQL Join between two tables two columns, but the data in the join condition could be null.

Question

hello all,
can anyone help me write an outer join b/n the two tables below. The joining condition has if's and or's.
table 1 has 2 million rows, table 2 is very small
TABLE1
CUSTOMER_ID
CITY
STATE
1
SKOKIE
IL
2
CHICAGO
IL
3
CARY
NC
ERIE
PA
PHILLY
PA
CHARLOTE
NC
2 MILLION
CITYXY
STATEX
TABLE2
CITY
STATE
CONTACT
IL
OJO
ERIE
BRITT
PA
MIKE
PITTSBURG
PA
HILTON
N043
TAT
affi
B
affi
R
b0b
Q
b0b
CHARLOTE
NC
b0b
problem :: for all the data in table1, I need to find out the CONTACT from table 2 And the join condition would be as below
1. either both TABLE1.CITY=TABLE2.CITY AND TABLE1.STATE=TABLE2.STATE and get CONTACT
OR
2. TABLE1.CITY=TABLE2.CITY AND TABLE2.STATE IS NULL  and get the value of CONTACT
OR
3. TABLE1.STATE=TABLE2.STATE AND TABLE2.CITY is null and get the value of CONTACT
I need a query like this
SELECT A.CUSTOMER_ID, A.CITY, A.STATE, B.CONTACT
FROM TABLE1 A, TABLE2 B
WHERE (join condition fitting in the 3 condition mentioned above)

Answer 1

Dear OP,
Do you want something like this?
> with t1 as
-- Start of SAMPLE DATA
(select 1 CUSTOMER_ID, 'SKOKIE' CITY, 'IL' STATE from dual union
select 2, 'CHICAGO', 'IL'  from dual union
select 3, 'CARY', 'NC' from dual union
select 4, 'ERIE', 'PA'  from dual union
select 5, 'PHILLY', 'PA'  from dual union
select 6, 'CHARLOTE', 'NC' from dual)
t2 as
(select null CITY, 'IL' STATE, 'OJO' CONTACT from dual union
select  'ERIE', null, 'BRITT'  from dual union
select null, 'PA', 'MIKE'  from dual union
select 'PITTSBURG', 'PA', 'HILTON'  from dual union
select 'N043', 'TAT', 'affi'  from dual union
select null,'B', 'affi'  from dual union
select null,'R', 'b0b'  from dual union
select null,'Q', 'b0b'  from dual union
select 'CHARLOTE', 'NC', 'b0b'  from dual
--- END IF SAMPLE Data
select * from t1 full outer join t2
on ( nvl(t1.city,t2.city) = nvl(t2.city,t1.city)
and nvl(t1.state,t2.state) = nvl(t2.state,t1.state) )
order by 1,2,3,4
CUSTOMER_ID CITY     STATE CITY      STATE CONTACT
          1 SKOKIE   IL              IL    OJO    
          2 CHICAGO  IL              IL    OJO    
          3 CARY     NC                           
          4 ERIE     PA    ERIE            BRITT  
          4 ERIE     PA              PA    MIKE   
          5 PHILLY   PA              PA    MIKE   
          6 CHARLOTE NC    CHARLOTE  NC    b0b    
                           N043      TAT   affi   
                           PITTSBURG PA    HILTON 
                                     B     affi   
                                     Q     b0b    
                                     R     b0b    
12 rows selected
Elapsed: 00:00:00.112
Hope this is helpful. If not please let us know what is you desired result (sample) if your data was like above?
vr,
Sudhakar