Trying to get newest record using a select statement

Question

Hello everyone.. I'm a bit new at this but I've been teaching myself by trial and error so bear with me.
Using a 'DEDUCTION' table for this example, I am trying to get it to resolve the record that is most current. Since each employee record could have changes, the table could have multiple entries/deductions of which only one is the most current.
Ok, so medical deductions are like DEDUCTIONS 700-715 while dental deductions are 730-737. Initially, I was trying to figure out how to pull the deductions based on an employee and have it compare which is newer and report the newest one for each medical and then the dental deduction. If there is not a type of deduction for someone, it should report zero like a NVL I think. See example:
EMP_ID DEDUCTIONS EFF_DATE AMT
1 710 2000/12/01 85.39
1 735 2000/12/01 8.31
9 701 2001/08/29 12
9 707 2000/12/01 12
9 730 2000/12/01 .23
10 700 2001/02/25 .46
10 730 2001/02/25 .23
The record that stands out in this example is employee #9 with two medical deduction, one that supersedes the other - 701 and 707. Because 701 is newer it should ignore the 707 deduction.
Any ideas? Thank you!
ken

Answer 1

Here are a couple of methods. The second one should run faster, but requires Oracle 8i.
SQL> SELECT   emp_id, deductions, eff_date, amt,
  2           'MEDICAL' AS type
  3  FROM     deduction
  4  WHERE    (emp_id, eff_date) IN
  5           (SELECT   emp_id, MAX (eff_date)
  6            FROM     deduction
  7            WHERE    deductions BETWEEN 700 AND 715
  8            GROUP BY emp_id)
  9  AND      deductions BETWEEN 700 AND 715
10  UNION
11  SELECT   emp_id, deductions, eff_date, amt,
12           'DENTAL' AS type
13  FROM     deduction
14  WHERE    (emp_id, eff_date) IN
15           (SELECT   emp_id, MAX (eff_date)
16            FROM     deduction
17            WHERE    deductions BETWEEN 730 AND 737
18            GROUP BY emp_id)
19  AND      deductions BETWEEN 730 AND 737
20  ORDER BY emp_id, deductions
21  /
    EMP_ID DEDUCTIONS EFF_DATE          AMT TYPE
         1        710 2000/12/01      85.39 MEDICAL
         1        735 2000/12/01       8.31 DENTAL
         9        701 2001/08/29         12 MEDICAL
         9        730 2000/12/01        .23 DENTAL
        10        700 2001/02/25        .46 MEDICAL
        10        730 2001/02/25        .23 DENTAL
6 rows selected.
SQL> SELECT   emp_id, deductions, eff_date, amt,
  2           'MEDICAL' AS type
  3  FROM     (SELECT   emp_id, deductions, eff_date, amt,
  4                     RANK () OVER
  5                          (PARTITION BY emp_id
  6                           ORDER BY     eff_date DESC) AS rk
  7            FROM     deduction
  8            WHERE    deductions BETWEEN 700 AND 715)
  9  WHERE    rk = 1
10  UNION
11  SELECT   emp_id, deductions, eff_date, amt,
12           'DENTAL' AS type
13  FROM     (SELECT   emp_id, deductions, eff_date, amt,
14                     RANK () OVER
15                          (PARTITION BY emp_id
16                           ORDER BY     eff_date DESC) AS rk
17            FROM     deduction
18            WHERE    deductions BETWEEN 730 AND 737)
19  WHERE    rk = 1
20  ORDER BY emp_id, deductions
21  /
    EMP_ID DEDUCTIONS EFF_DATE          AMT TYPE
         1        710 2000/12/01      85.39 MEDICAL
         1        735 2000/12/01       8.31 DENTAL
         9        701 2001/08/29         12 MEDICAL
         9        730 2000/12/01        .23 DENTAL
        10        700 2001/02/25        .46 MEDICAL
        10        730 2001/02/25        .23 DENTAL
6 rows selected.