Pickup the Latest Result Date (Query involves 3 tables)

Question

Hello folks,
I have a relatively simple request. It involves 3 simple tables. I want to return the Student along with the Results based on the Latest Result Date and a Flag. Any help is appreciated.
Thanks
Assumptions
STUDENT_ID is unique in STUDENT_TB
EXAM_VISIT_ID is Unique in EXAM_RESULTS_TB.
Scripts for table creation and INSERT statements
create table student_tb (student_id varchar2(4));
create table exam_tb (student_id varchar2(4), exam_visit_id number, exam_date date);
create table exam_results (exam_visit_id number, result_date date, results number, result_flag varchar2(1));
insert into student_tb values('1001');
insert into student_tb values('1002');
Insert into EXAM_TB (STUDENT_ID,EXAM_DATE,EXAM_VISIT_ID) values ('1001',to_date('01-JAN-12','DD-MON-RR'),1);
Insert into EXAM_TB (STUDENT_ID,EXAM_DATE,EXAM_VISIT_ID) values ('1001',to_date('01-APR-12','DD-MON-RR'),2);
Insert into EXAM_TB (STUDENT_ID,EXAM_DATE,EXAM_VISIT_ID) values ('1001',to_date('01-JUL-12','DD-MON-RR'),3);
Insert into EXAM_TB (STUDENT_ID,EXAM_DATE,EXAM_VISIT_ID) values ('1001',to_date('01-SEP-12','DD-MON-RR'),4);
Insert into EXAM_RESULTS_TB (EXAM_VISIT_ID,RESULT_DATE,FLAG,RESULTS) values (1,to_date('01-FEB-12','DD-MON-RR'),'N',10);
Insert into EXAM_RESULTS_TB (EXAM_VISIT_ID,RESULT_DATE,FLAG,RESULTS) values (2,to_date('01-MAY-12','DD-MON-RR'),'Y',40);
Insert into EXAM_RESULTS_TB (EXAM_VISIT_ID,RESULT_DATE,FLAG,RESULTS) values (3,to_date('01-AUG-12','DD-MON-RR'),'Y',32);
Insert into EXAM_RESULTS_TB (EXAM_VISIT_ID,RESULT_DATE,FLAG,RESULTS) values (4,to_date('01-DEC-12','DD-MON-RR'),'N',20);I would like to pick up the Student along with the RESULT_DATE and RESULTS where the RESULT_DATE (EXAM_DATE is irrelevant for this exercise) is the most recent for that Student and the flag = 'Y'. EXAM_VISIT_ID is Unique. So, the record that needs to be returned from this Result set is
1001 3 01-AUG-12 32

Answer 1

Hi,
That's an example of a Top-N Query , and here's one way to do it:
WITH   got_r_num   AS
     SELECT  e.student_id, e.exam_visit_id
     ,     er.result_date, er.results
     ,     RANK () OVER ( PARTITION BY  e.student_id
                           ORDER BY          er.result_date  DESC
                    )           AS r_num
     FROM    exam_tb              e
     JOIN     exam_results_tb  er  ON   er.exam_visit_id  = e.exam_visit_id
     WHERE     er.flag     = 'Y'
SELECT  student_id, exam_visit_id
,     result_date, results
FROM     got_r_num
WHERE     r_num     = 1
;Thanks for posting the CREATE TABLE and INSERT statements. Please make sure they work before posting them. There is some confusion about the table (EXAM_RESULTS or EXAM_RESULTS_TB) and column (FLAG or RESULT_FLAG) names.
What results do you want if there is a tie for the most recent exam for a given student? (E.g., if we change the result_date on this row
Insert into EXAM_RESULTS_TB (EXAM_VISIT_ID,RESULT_DATE,FLAG,RESULTS) values (2,to_date('01-MAY-12','DD-MON-RR'),'Y',40);to be August 1, 2012, just like the row with exam_visit_id=3)?
Depending on your requirements, you may want to add tie-breaking columns to the end of the analytic ORDER BY clause, and/or use ROW_NUMBER instead of RANK.