Hello,
you can use the STRING_AGG aggregation function.
If "Header 1" column name is e.g. "COL1" and "Header 2" column name is e.g. "COL2" the statement would look like following.
SELECT "COL1", STRING_AGG("COL2",', ')
FROM <schema>.<table>
GROUP BY "COL1";Best Regards,
Florian