问在Postgres SQL中，如何将值转换为范围并获得最大记录的范围

EN

SELECT (CASE WHEN age BETWEEN 7 AND 9 THEN '7-9'
           WHEN age BETWEEN 10 AND 12 THEN '10-12'
           WHEN age BETWEEN 13 AND 15 THEN '13-15'
           WHEN age BETWEEN 15 AND 17 THEN '15-17'
           WHEN age BETWEEN 17 AND 19 THEN '17-19' END) as range,
      COUNT(*) cnt
FROM students
GROUP BY  CASE WHEN age BETWEEN 7 AND 9 THEN '7-9'
           WHEN age BETWEEN 10 AND 12 THEN '10-12'
           WHEN age BETWEEN 13 AND 15 THEN '13-15'
           WHEN age BETWEEN 15 AND 17 THEN '15-17'
           WHEN age BETWEEN 17 AND 19 THEN '17-19' END
ORDER BY COUNT(*) DESC 
LIMIT 1

SELECT CONCAT(t1.startnum,'-',t1.endnum) as range,
      COUNT(*) cnt
FROM students s
INNER JOIN (
    SELECT v startnum,v+2 endnum
    FROM generate_series(7,17,2) v 
  ) t1 ON s.age BETWEEN t1.startnum AND t1.endnum
GROUP BY CONCAT(t1.startnum,'-',t1.endnum)
ORDER BY COUNT(*) DESC 
LIMIT 1

CREATE TABLE age_range (
    id serial,
    agerange numrange
);

INSERT INTO age_range (agerange)
    VALUES ('[7,9]'), ('[10,12]'), ('[13,15]'), ('[15,17]'), ('[17,19]');

  WITH a AS (
    SELECT
        age,
        name,
        agerange
    FROM
        students s,
        age_range b
    WHERE
        age <@ agerange IS TRUE
)
SELECT
    *,
    count(agerange) OVER (PARTITION BY agerange)
FROM
    a
ORDER BY
    agerange,
    name;