string aggexpression delimiter

You can concatenate strings separated by delimiter using the string_agg() function.

If your individuals table is:

Name | Age| Country |
–– | —| –– |
Allie | 15 | USA |
Amanda | 14 | USA |
Alana | 20 | Russia |

You could write SELECT ... GROUP BY statement to get names from each country:

SELECT string_agg(name, ', ') AS names, country 
FROM individuals 
GROUP BY country;

Note that you need to use a GROUP BY clause because string_agg() is an aggregate function.

Result:

names | country |
—– | —–– |
Allie, Amanda | USA |
Alana | Russia |

More PostgreSQL aggregate function described here