How to select data with multiple child nodes

Question

We have the following data:
me table ei table
m1 e1
m1 e2
m1 e3
m1 e4
m2 e5
m2 e6
m3 e7
m3 e8
I would like to display them as:
m1 e1
e2
e3
e4
m2 e5
e6
m3 e7
e8
How to best do this with sql?
I would like to produce this list with sql and then transform it to xml.
Thanks.

Answer 1

Since you did not use tags it is not clear what results should be:
SQL> WITH TBL AS (
  2  SELECT 'm1' me, 'e1' ei FROM DUAL UNION ALL
  3  SELECT 'm1' me, 'e2' ei FROM DUAL UNION ALL
  4  SELECT 'm1' me, 'e3' ei FROM DUAL UNION ALL
  5  SELECT 'm1' me, 'e4' ei FROM DUAL UNION ALL
  6  SELECT 'm2' me, 'e5' ei FROM DUAL UNION ALL
  7  SELECT 'm2' me, 'e6' ei FROM DUAL UNION ALL
  8  SELECT 'm3' me, 'e7' ei FROM DUAL UNION ALL
  9  SELECT 'm3' me, 'e8' ei FROM DUAL
10  )
11  SELECT  CASE ROW_NUMBER() OVER(PARTITION BY ME ORDER BY EI) WHEN 1 THEN ME ELSE NULL END ME,
12          EI
13    FROM  TBL
14    ORDER BY TBL.ME,
15             TBL.EI
16  /
ME EI
m1 e1
   e2
   e3
   e4
m2 e5
   e6
m3 e7
   e8
8 rows selected.or
SQL> WITH TBL AS (
2 SELECT 'm1' me, 'e1' ei FROM DUAL UNION ALL
3 SELECT 'm1' me, 'e2' ei FROM DUAL UNION ALL
4 SELECT 'm1' me, 'e3' ei FROM DUAL UNION ALL
5 SELECT 'm1' me, 'e4' ei FROM DUAL UNION ALL
6 SELECT 'm2' me, 'e5' ei FROM DUAL UNION ALL
7 SELECT 'm2' me, 'e6' ei FROM DUAL UNION ALL
8 SELECT 'm3' me, 'e7' ei FROM DUAL UNION ALL
9 SELECT 'm3' me, 'e8' ei FROM DUAL
10 )
11 SELECT CASE ROW_NUMBER() OVER(PARTITION BY ME ORDER BY EI) WHEN 1 THEN ME ELSE EI END ME,
12 CASE ROW_NUMBER() OVER(PARTITION BY ME ORDER BY EI) WHEN 1 THEN EI ELSE NULL END EI
13 FROM TBL
14 ORDER BY TBL.ME,
15 TBL.EI
16 /
ME EI
m1 e1
e2
e3
e4
m2 e5
e6
m3 e7
e8
8 rows selected.
SQL>
SY.