Recursive query in DB2 to get all items in the chain

Question

I have to retrieve all clients linked via loans by giving only one as input. Example I have a table data as

TABLEA

LOAN_ID    CLIENT_ID
1          7
1          8
2          7
4          8
4          9
4         10
5          9
5         11
13        2
14        3

If I have given only input as CLIENT_ID=7 then the query has to select all the columns from above table except last two column because client_id 7 has 1,2 LOAN_ID and in 1 the CLIENT_ID 8 has loan_id=4 and in this loan CLIENT_id 9 has again 5 as loan_id.

can we write a sql query for this without stored procedure in DB2 ?

Answer 1

Here is the answer to your question using recursive CTE query:

WITH links AS
( SELECT 
    loan_id, 
    client_id as c1, 
    client_id as c2, 0 as distance 
  FROM 
    myTable 
  -- recursion 
  UNION ALL
  SELECT 
     t.loan_id, 
     l.c1 as c1, 
     tt.client_id as c2, 
     distance = distance + 1 
  FROM 
    links l INNER JOIN
    myTable t ON l.c2 = t.client_id
    AND l.loan_id != t.loan_id INNER JOIN
    myTable tt  ON t.loan_id = tt.loan_id 
     AND t.client_id != tt.client_id
 )
SELECT * FROM myTable t
WHERE EXISTS 
    (SELECT * FROM links 
     WHERE c2 = t.client_id and c1 = 7);

http://sqlfiddle.com/#!3/8394d/16

I have left distance inside the query to make it easier to understand.