Getting specific row of the result set.

Question

table: employee
empno           number(20)
ssan           varchar2(9)
date_time_stamp date
My Sql gets all the empno where ssan and date_time_stamp are equal.
However I need previous row from max(empno) where ssan & date_time_stamp are equal.
For eg:
empno     ssan           date_time_stamp
100     123456789     01-FEB-2004
101     000000000     02-FEB-2004
102     123456789     01-FEB-2004
103     123456789     01-FEB-2004
105     123456789     01-FEB-2004
I need row with empno = 103.
My current sql fetches all rows for particular ssan where ssan and date time stamp are equal that fetches all empno for particular ssan and date time stamp. I want the max(empno) -1 (previous row of the result set).
Here is my sql:
select empno,ssan,date_time_stamp
from employee e
where date_time_stamp in (select date_time_stamp from employee where e.ssan = ssan)
order by empno,ssan;
The above sql will fetch
empno     ssan           date_time_stamp
100     123456789     01-FEB-2004
102     123456789     01-FEB-2004
103     123456789     01-FEB-2004 ---> I need this row, previous row from max(empno) where ssan and date time
stamp are matching.
105     123456789     01-FEB-2004
101     000000000     02-FEB-2004

Answer 1

If I understand correctly, you want the second highest empno for each unique combination of ssan and date_time_stamp. If so, given
SQL> SELECT * FROM employee;
     EMPNO SSAN      DATE_TIME_S
       102 123456789 01-feb-2004
       103 123456789 01-feb-2004
       105 123456789 01-feb-2004
       100 123456678 01-feb-2004
       102 123456678 01-feb-2004
       103 123456678 01-feb-2004
       101 000000000 02-feb-2004
       105 123456678 01-feb-2004
       100 123456678 02-feb-2004
       102 123456678 02-feb-2004
       103 123456678 02-feb-2004
       105 123456678 02-feb-2004
       100 123456789 01-feb-2004Then something like this should do it.
SQL> SELECT empno,ssan,date_time_stamp
  2  FROM (SELECT empno,ssan,date_time_stamp,
  3               RANK() OVER (PARTITION BY ssan,date_time_stamp
  4                            ORDER BY empno DESC) rk
  5        FROM employee)
  6* WHERE rk = 2;
     EMPNO SSAN      DATE_TIME_S
       103 123456678 01-feb-2004
       103 123456678 02-feb-2004
       103 123456789 01-feb-2004HTH
John