How to convert single column into single row

Question

I need to convert single column into single row having n no.of.values in a column. without using case or decode. I need a query to display as below.
emp_id
100
101
102
102
103
200
I need output like 100,101,102,103,104.........200.

Answer 1

I assume you want to convert 200 rows with one column into one row with 200 columns. If so, this is called pivot. If you know number of rows (max possible number of rows) and you are on 11G you can use PIVOT operator (on lower versions GROUP BY + CASE). Otherwise, if row number isn't known, you can use dynamic SQL or assemble select on clent side. Below is example emp_id = 1,2,..5 (to give you idea) and you are on 11G:
with emp as (
             select  level emp_id
               from  dual
               connect by level <= 5
select  *
  from  emp
  pivot(
        max(emp_id) for emp_id in (1 emp_id1,2 emp_id2,3 emp_id3,4 emp_id4,5 emp_id5)
   EMP_ID1    EMP_ID2    EMP_ID3    EMP_ID4    EMP_ID5
         1          2          3          4          5
SQL>
SY.