SQL语句 按年龄段分组统计人数问题

 

SELECT
	CASE
WHEN age IS NULL THEN
	'未知'
WHEN age < 20 THEN
	'小于20岁'
WHEN age >= 20
AND age < 30 THEN
	'20岁到30岁'
WHEN age >= 30
AND age < 40 THEN
	'30岁到40岁'
WHEN age >= 40
AND age < 50 THEN
	'40岁到50岁'
WHEN age >= 50 THEN
	'50岁以上'
END AS 年龄段,
 count(*) AS 人数
FROM
	user
GROUP BY
	CASE
WHEN age IS NULL THEN
	'未知'
WHEN age < 20 THEN
	'小于20岁'
WHEN age >= 20
AND age < 30 THEN
	'20岁到30岁'
WHEN age >= 30
AND age < 40 THEN
	'30岁到40岁'
WHEN age >= 40
AND age < 50 THEN
	'40岁到50岁'
WHEN age >= 50 THEN
	'50岁以上'
END;

运行结果：