Please help me constructing this query

Question

please help me .
     table a          
     ===========          
transactionid     personname     year     dept
r001          person1          y1     d1
r002          person1          y2     d2
r005          person3          y1     d2
r004          person2          y2     d1
     table b     
     ===========     
transactionid     personname     year
r005          person3          y2
r006          person4          y1
r001          person1          y1
     outout should be like                         
     ======================                         
transactionid     personname     year     dept               
r001          person1          y1     d1     record present (combination of transactionid/personname/year)in table a from table b          
r005          person3          y2     d2     (no data present in table a (transactionid/personname/year) from table b
so it will retrive previous dept records for this person for this year so here d2)          
r006          person4          y1     unknown     no data present for this person in table a so department will be unknown          
table creation script
=====================
CREATE TABLE A
TRANSACTIONID VARCHAR2(30 BYTE),
PERSONNAME VARCHAR2(30 BYTE),
YEAR VARCHAR2(30 BYTE),
DEPT VARCHAR2(30 BYTE)
SET DEFINE OFF;
Insert into A
(TRANSACTIONID, PERSONNAME, YEAR, DEPT)
Values
('r001', 'person1', 'y1', 'd1');
Insert into A
(TRANSACTIONID, PERSONNAME, YEAR, DEPT)
Values
('r002', 'person1', 'y2', 'd2');
Insert into A
(TRANSACTIONID, PERSONNAME, YEAR, DEPT)
Values
('r004', 'person2', 'y2', 'd1');
Insert into A
(TRANSACTIONID, PERSONNAME, YEAR, DEPT)
Values
('r005', 'person3', 'y1', 'd2');
COMMIT;
CREATE TABLE B
TRANSACTIONID VARCHAR2(30 BYTE),
PERSONNAME VARCHAR2(30 BYTE),
YEAR VARCHAR2(30 BYTE)
SET DEFINE OFF;
Insert into B
(TRANSACTIONID, PERSONNAME, YEAR)
Values
('r001', 'person1', 'y1');
Insert into B
(TRANSACTIONID, PERSONNAME, YEAR)
Values
('r006', 'person4', 'y1');
Insert into B
(TRANSACTIONID, PERSONNAME, YEAR)
Values
('r005', 'person3', 'y2');
COMMIT;

Answer 1

Anirudha Dhopate wrote:
Following query should work - Data magic:
SQL> SELECT  *
  2    FROM  a
  3  /
TRANSACTIONID        PERSONNAME YEAR  DEPT
r001                 person1    2010  d1
r002                 person1    2011  d2
r004                 person2    2011  d1
r005                 person3    2010  d2
r001                 person1    2010  d2
SQL> SELECT  *
  2    FROM  b
  3  /
TRANSACTIONID        PERSONNAME YEAR
r001                 person1    2010
r006                 person4    2010
r005                 person3    2011
SQL> SELECT b.transactionid
  2        ,b.personname
  3        ,b.year
  4        ,a.dept
  5    FROM a
  6   RIGHT OUTER JOIN b
  7      ON ((a.transactionid = b.transactionid) AND
  8         (a.personname = b.personname) AND
  9         (a.year = b.year OR a.year = b.year - 1))
10     ORDER BY b.transactionid
11  /
TRANSACTIONID        PERSONNAME YEAR  DEPT
r001                 person1    2010  d1
r001                 person1    2010  d2
r005                 person3    2011  d2
r006                 person4    2010
SQL> select  b.transactionid,
  2          b.personname,
  3          b.year,
  4          max(a.dept) keep(dense_rank last order by a.year) dept
  5    from      b
  6          left join
  7              a
  8            on (
  9                    b.transactionid = a.transactionid
10                and
11                    b.personname = a.personname
12                and
13                    b.year >= a.year
14               )
15    group by b.transactionid,
16             b.personname,
17             b.year
18  /
TRANSACTIONID        PERSONNAME YEAR  DEPT
r001                 person1    2010  d2
r005                 person3    2011  d2
r006                 person4    2010
SQL> SY.