Single query for querying three tables

Question

Hi All,
We are trying to construct a sql query(a single query), which can perform the below functionality.
Assume, that there are three tables,
TABLE1: 3 Columns
1) ID -> PRIMARY KEY
2) TYPE -> Allows only values 'A' or 'B'
3) REF_ID(this can refer to TABLE2(ID) or TABLE3(ID)).
TABLE2: 2 Columns
1) ID -> PRIMARY KEY
2) DETAILS -> Any normal text
TABLE3: 2 Columns
1) ID -> PRIMARY KEY
2) DETAILS -> Any normal text
We need to come up with a query that, given TABLE1's(ID), we need to fetch the corresponding record in TABLE1, and we need to fetch the corresponding record from TABLE2 or TABLE3, depending on the below conditions.
If the TYPE for the TABLE1's(ID) is 'A'
Then get the details from TABLE2's by mapping TABLE1.REF_ID = TABLE2.ID
If the TYPE for the TABLE1's(ID) is 'B'
Then get the details from TABLE3's by mapping TABLE1.REF_ID = TABLE3.ID
We need to accomplish all these tasks in a single query.
Thanks for your kindly help,
Sreenivasan

Answer 1

SQL> select * from test_qry1;
ID T REF_ID
1 A 100
2 A 200
3 B 300
SQL> select * from test_qry2;
ID DETAILS
100 Human Resources
200 It Services
300 Relationships
SQL> select * from test_qry3;
ID DETAILS
100 Human Beings
200 Conference
300 Used things
SQL> SELECT t1.ID,
DECODE(t1.type,'A',( SELECT t2.details FROM test_qry2 t2 WHERE t1.ref_id = t2.id
'B',( SELECT t3.details FROM test_qry3 t3 WHERE t1.ref_id = t3.id
) details
FROM test_qry1 t1;
ID DETAILS
1 Human Resource
2 It Services
3 Used things
Try with this query.
Thanks,
Vissu......