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