您需要一个年龄表来填充没有匹配行的条目的结果。这可以通过实际表完成，也可以通过子查询动态生成，如下所示：
SELECt a.ageband, IFNULL(t.agecount, 0)FROM ( -- ORIGINAL QUERY SELECt CASE WHEN age IS NULL THEN 'Unspecified' WHEN age < 18 THEN '<18' WHEN age >= 18 AND age <= 24 THEN '18-24' WHEN age >= 25 AND age <= 30 THEN '25-30' WHEN age >= 31 AND age <= 40 THEN '31-40' WHEN age > 40 THEN '>40' END AS ageband, COUNT(*) as agecount FROM (SELECt age FROM Table1) t GROUP BY ageband) tright join ( -- TABLE OF POSSIBLE AGEBANDS SELECT 'Unspecified' as ageband union SELECT '<18' union SELECT '18-24' union SELECT '25-30' union SELECT '31-40' union SELECT '>40') a on t.ageband = a.ageband
演示：http ://www.sqlfiddle.com/#!2/
7e2a9/10
