如何在Postgres中按行数分组？

SELECT 
    CASE 
        WHEN row_number() OVER (ORDER BY column_name) <= 10 THEN 'Group 1'
        WHEN row_number() OVER (ORDER BY column_name) <= 20 THEN 'Group 2'
        ELSE 'Group 3'
    END AS group_name,
    column_name
FROM 
    table_name
ORDER BY 
    column_name;