Rows to columns wise query

Oracle 9i xmlagg

In Oracle 9i we can use the xmlagg function to aggregate multiple rows onto one column:

select
deptno,
rtrim (xmlagg (xmlelement (e, ename || ',')).extract ('//text()'), ',') enames
from
emp
group by
deptno
;

DEPTNO ENAMES
---------- ----------------------------------------
10 CLARK,MILLER,KING
20 SMITH,FORD,ADAMS,SCOTT,JONES
30 ALLEN,JAMES,TURNER,BLAKE,MARTIN,WARD



Use 11g SQL pivot for single row output


The SQL pivot operator allows you to take multiple rows and display them on a single line.

select *
from
(select fk_department
from employee)
pivot
(count(fk_department)
for fk_department in ('INT', 'WEL', 'CEN', 'POL'));

'INT' 'WEL' 'CEN' 'POL'
---------- ---------- ---------- -------
7 6 0 8


Use SQL within group for moving rows onto one line and listagg to display multiple column values in a single column

In Oracle 11g, we have the within group SQL clause to pivot multiple rows onto a single row. We also a have direct SQL mechanism for non first-normal form SQL display. This allows multiple table column values to be displayed in a single column, using the listagg built-in function :

select
deptno,
listagg (ename, ',')
WITHIN GROUP
(ORDER BY ename) enames
FROM
emp
GROUP BY
deptno
/
DEPTNO ENAMES
---------- --------------------------------------------------
10 CLARK,KING,MILLER
20 ADAMS,FORD,JONES,SCOTT,SMITH
30 ALLEN,BLAKE,JAMES,MARTIN,TURNER,WARD


Use the SYS_CONNECT_BY_PATH operator



select
deptno,
substr(SYS_CONNECT_BY_PATH(lname, ','),2) name_list
from
(
select
lname,
deptno,
count(*) OVER ( partition by deptno ) cnt,
ROW_NUMBER () OVER ( partition by deptno order by lname) seq
from emp
where
deptno is not null)
where
seq=cnt
start with
seq=1
connect by prior
seq+1=seq
and prior
deptno=deptno;

DEPTNO NAME_LIST
1 Komers,Mokrel,Stenko
2 Hung,Tong
3 Hamer
4 Mansur


Use a Cross join


Matt contributed this handy SQL techniques to pivot one row of several columns into a single column with several row, using the Oracle Cross join syntax. Matt notes that the Cross join "has other uses in conjunction with a WHERE clause to create triangular result sets for rolling totals etc (though thanks to analytic functions those things are very nice and easy)".

SELECT
ite,
case
when ite = 'item1' then item1
when ite = 'item2' then item2
when ite = 'item3' then item3
end as val
FROM
(
SELECT
pivoter.ite,
item1,
item2,
item3
FROM
someTable
CROSS JOIN
(
select 'item1' as ite from dual
UNION ALL
select 'item2' as ite from dual
UNION ALL
select 'item3' as ite from dual
)pivoter
)



Use the Oracle analytic Lag-Over Function


Analytic functions have a pronounced performance improvement since they avoid an expensive self-join and only make one full-table scan to get the results. This site shows an example of using the Oracle LAG function to display multiple rows on a single column:

SELECT
ename,
hiredate,sal,LAG (sal, 1, 0)
OVER (ORDER BY hiredate) AS PrevSal
FROM
emp
WHERE
job = 'CLERK';

Use the SQL CASE operator to pivot rows onto one line

You can use the CASE statement to create a crosstab to convert the rows to columns. Below, the Oracle CASE function to create a "crosstab" of the results, such as this example from SearchOracle:

select Sales.ItemKey
, sum(Sales.QtySold) as Qty
, sum(
case when OH.MOHClass = 'Fixed'
then OH.Amt
else .00 end ) as MOHFixed
, sum(
case when OH.MOHClass = 'Var'
then OH.Amt
else .00 end ) as MOHVar
, sum(
case when OH.MOHClass = 'Cap'
then OH.Amt
else .00 end ) as MOHCap
from Sales
left outer
join OH
on Sales.ItemKey = OH.ItemKey
group
by Sales.ItemKey