oracle用sql语句实现年龄分段统计，case when then用法(用于分类统计)

sql 对一张表进行按照不同条件进行多次统计
在这里使用 case when then(多用于分类统计)

SELECT
	CASE
WHEN age < 30 THEN
	'30岁以下'
WHEN age BETWEEN 30
AND 35 THEN
	'30-35岁'
WHEN age BETWEEN 36
AND 40 THEN
	'36-40岁'
WHEN age > 40 THEN
	'40岁以上'
END AS NAME,
 count(*) AS count
FROM
	(
		SELECT
			(
				SELECT
					to_number (to_char(sysdate, 'yyyy'))
				FROM
					DUAL
			) - substr(csny, 0, 4) AS age
		FROM
			t_xwr_lz_grxx b,
			t_xwr_sys_user c,
			t_xwr_sys_dept d
		WHERE
			b.xm = c.user_id
		AND c.dept_id = d.dept_id
		AND (
			SELECT
				to_number (to_char(sysdate, 'yyyy'))
			FROM
				DUAL
		) - substr(csny, 0, 4) IS NOT NULL
	)
GROUP BY
	CASE
WHEN age < 30 THEN
	'30岁以下'
WHEN age BETWEEN 30
AND 35 THEN
	'30-35岁'
WHEN age BETWEEN 36
AND 40 THEN
	'36-40岁'
WHEN age > 40 THEN
	'40岁以上'
END;

解释以下：

由于数据库里没有年龄字段，这里只能由 获取当年年份 - 出生年
所有有了这个写法： 当年年份 - 出生年
(select to_number(to_char(sysdate, ‘yyyy’ )) from dual) - substr(csny,0,4) as age

结果如下所示