mysql 按某字段分組分箱聚合查詢

SELECT cidnum1,count(*) as num from 
(
SELECT DISTINCT id,cidnum,
(CASE 
        WHEN 0<cidnum and cidnum<=1 THEN '1個公司'
        WHEN 1<cidnum and cidnum<=5 THEN '2-5個公司'
        WHEN 5<cidnum and cidnum<=10 THEN '6-10個公司'
        when 10<cidnum and cidnum<=50 then '11-50個公司'
        when 50<cidnum and cidnum<=100 then '51-100個公司'
        when 100<cidnum and cidnum<=500 then '101-500個公司'
        when 501<cidnum and cidnum<=1000 then '501-1000個公司'
        ELSE '1001個公司以上'
END) as cidnum1
FROM TABLE
where ***
) a
GROUP BY cidnum1
ORDER BY num desc