从两个DB2表UNION ALL中提取数据

Question

I have two tables.. In output result I want to merge data from both. So assume I have to use UNION statement. What I need in result set:

1. rows 1 and 2 from TABLE1 only.
2. all rows from TABLE2 where TABLE2/COL4 = TABLE1/COL1 in these were selected in #1, (these are 1 and 3 in TABLE2)
3. In output results substitute data in COL2 for TABLE2 rows with data from COL2 of TABLE1

 TABLE1------------------------------------------ COL1 COL2 COL3 1 aaa1 eee1 2 bbb1 fff1 3 ccc1 ggg1 4 ddd1 hhh1 TABLE2------------------------------------------ COL1 COL2 COL3 COL4 1 aaa2 eee2 1 2 bbb2 fff2 4 3 ccc2 ggg2 1 4 ddd2 hhh2 3 RESULT I NEED----------------------------------- COL1 COL2 COL3 1 aaa1 eee1 2 bbb1 fff1 1 aaa1 eee2 3 aaa1 ggg2 

I need something like this:

SELECT#1 COL1, COL2, COL3 FROM TABLE1 WHERE COL1 IN ('1','2')
UNION ALL
SELECT#2 COL1, COL2 <AS SELECT#1.COL2>, COL3 FROM TABLE2 WHERE <COL4 IN SELECT#1.COL1>

Answer 1

select col1, col2, col3 from table1
WHERE COL1 IN (1,2)
union
select t2.col1,
       coalesce((select col2 from table1
                 WHERE COL1 IN (1,2)
                   AND COL1 = t2.col4),
                t2.col2),
       t2.col3
from table2 t2 join table1 t1 on t1.col1 = t2.col1 and col4 in
  (select col1 from table1 WHERE COL1 IN (1,2))

Gives me:

SQL>select * from table1
SQL&WHERE COL1 IN (1,2)
SQL&union
SQL&select t2.col1,
SQL&       coalesce((select col2 from table1
SQL&                 WHERE COL1 IN (1,2)
SQL&                   AND COL1 = t2.col4),
SQL&                t2.col2),
SQL&       t2.col3
SQL&from table2 t2 join table1 t1 on t1.col1 = t2.col1 and col4 in
SQL&  (select col1 from table1 WHERE COL1 IN (1,2))
SQL&;

       col1 col2   col3
       ==== ====   ====
          1 aaa1   eee1
          2 bbb1   fff1
          1 aaa1   eee2
          3 aaa1   ggg2

4 rows found