Display Distinct Item Value

Question

Hello All,
I am having an problem displaying a distinct value for Item 'PK_EMPL_ID'. I need all the Items below because I am passing these values to another page in APEX. But I need help with this select statement syntax.
SELECT hs.pk_session_id,
       hsp.pk_session_process_id,
       hs.fk_class_id,
       hsm.pk_empl_id,
       hsm.last_name || ', ' || hsm.first_name studentname,
       dg.department_group_descr,
       pd.department_descr,
       hsm.fk_dept_group,
       hsm.fk_dept_code,
       hsp.fk_empl_id,
       hs.session_meridiem,
       hsn.session_name,
       hs.session_date,
       hsp.session_process_status
    FROM   hrt_session hs,
           hrt_session_name hsn,
           hrt_session_process hsp,
           hrt_student_master hsm,
           cobr.department_group dg,
           cobr.pps_department pd
    WHERE  hsn.pk_session_name_id = hs.fk_session_name_id
       AND hsp.fk_session_id = hs.pk_session_id
       AND hsp.fk_empl_id = hsm.pk_empl_id
       AND hsm.fk_dept_group = dg.pk_department_group_id
       AND hsm.fk_dept_code = pd.pk_department_idMy output is like:
-PK_EMPL_ID-
JOHN
JOHN
JOHN
BOBBY
JAMES
I only want to display each 'PK_EMPL_ID' value once when the select statement is executed, not duplicate values. I have tried distinct, group by etc... but I am having trouble since I am using multiple tables using these foreign keys. I have viewed a few threads but they are only handling one or two item values from one table. Can anyone assist me with please? Thanks ahead of time.

Answer 1

Hi,
Whenever you have a question, post a little sample data (CREATE TABLE and INSERT statements) for all tables, and the results uyou want from that data.
You may have a clear idea of where you're coming from, and where you want to go, but the description alone doesn't convey that clear idea to us.
You can also rephrase your question in terms of some commonly available table, like scott.emp.
For example: "I'm doing this query on scott.emp:
{code}
SELECT      job
,     deptno
FROM     scott.emp
{code}
How can I get only 1 row per distinct job?"
Without sample output, the question is still vague.
There are 14 rows in scott.emp.
You can reduce the output to 9 rows by changing "SELECT" to "SELECT *DISTINCT* ":
SELECT DISTINCT
     job
,     deptno
FROM     scott.emp
;which produces:
OB           DEPTNO
MANAGER           20
PRESIDENT         10
CLERK             10
SALESMAN          30
ANALYST           20
MANAGER           30
MANAGER           10
CLERK             30
CLERK             20But that's as far as you can go without changing the results.
For example, all three departments have MANAGERs. If you want only 5 rows of outptu (one for each of the 5 distinct jobs), then which deptno do you want?
If you want the lowest one, here's one way to do that:
WITH     got_rnum     AS
     SELECT     job
     ,     deptno
     ,     ROW_NUMBER () OVER ( PARTITION BY  job
                               ORDER BY          deptno
                       ) AS rnum
     FROM    scott.emp
SELECT     job
,     deptno
FROM     got_rnum
WHERE     rnum     = 1
;Output:
JOB           DEPTNO
ANALYST           20
CLERK             10
MANAGER           10
PRESIDENT         10
SALESMAN          30There are other apprioaches to this problem, too. The advantage of this one is that it works well with any number of columns in the output.