postgresql – Aggregate Functions – string_agg(expression, 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

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postgresql – Aggregate Functions – string_agg(expression, delimiter) - CodeDay