It's a common operation in DB to have a need of grouping and concatenating several columns in the output result of the query. For example if you want to get make an report for people based on their country from a table containing both the country and the person:

Example 1

On the left is the table and on the right is the concatenated output:

id	Name	Value	id	concat
1	A	3	1	A:3,B:2
1	B	2	2	C:6, R2
2	C	6	3	F:7
2	R	2	4	D:5
3	F	7
4	D	5

Example 2

On the left if the table that will be queried and on the right is the ouput result.


id	Country	Person	country	GROUP_CONCAT(person)
1	Austria	Sue	Ausria	Sue, Anie
2	Austria	Anie	Australia	John, Brian
3	Australia	John	UK	Jim, Tim
4	Australia	Brian	USA	David, Mike, Tom
5	UK	Jim	N. Korea	Joe, Hue, Rick, Jamy
6	UK	Tim	Finland	Kimi
7	USA	David
8	USA	Mike
9	USA	Tom
10	N. Korea	Joe
11	N. Korea	Hue
12	N. Korea	Rick
13	N. Korea	Jamy
14	Finland	Kimi

Oracle group concatenate

This is the oracle version of group concatenation by using the LISTAGG function. As you can see from the code below two things has to be given : the grouping column and the concatenating one.

SELECT country,
  LISTAGG(person, ', ') WITHIN GROUP (
ORDER BY person) "names"
FROM mytable
GROUP BY country;

MySQL concat and group

The mysql version is much simpler by using function GROUP_CONCAT and the example is self-explantory.

SELECT country, GROUP_CONCAT(person) FROM mytable GROUP BY country

country	GROUP_CONCAT(person)
Ausria	Sue, Anie
Australia	John, Brian
UK	Jim, Tim
USA	David, Mike, Tom
N. Korea	Joe, Hue, Rick, Jamy