text: SELECT CASE WHEN population < 100 THEN '01'
              WHEN population >= 100 AND population < 200 THEN '02'
              WHEN population >= 200 AND population < 300 THEN '03'
              WHEN population >= 300 THEN '04'
              ELSE NULL END AS pop_class,
         COUNT(*) AS cnt
    FROM PopTbl
   GROUP BY CASE WHEN population < 100 THEN '01'
                 WHEN population >= 100 AND population < 200 THEN '02'
                 WHEN population >= 200 AND population < 300 THEN '03'
                 WHEN population >= 300 THEN '04'
                 ELSE NULL END;