listagg 字符串连接的结果过长问题解决

因为业务需要对一些数据进行统计，需要对表涉及到的不同部门的进行过任务的用户id进行拼接之后到java代码中进行去重计数。

开始准备使用WM_CONCAT，放进去之后发现提示没有这个函数。

查了一下原来是因为这个函数依赖WMSYS用户，这个版本并没有配置，无奈只能退而求其次选择了listagg函数。

一轮下来效果不错，想要的效果可以实现。

SELECT
	r.department_id law_dept_id,
	(
		SELECT
			listagg (
				rt.extracted_person_ids,
				","
			) WITHIN GROUP (
				ORDER BY
 					rt.extracted_person_ids
			)
			
		FROM
			RANDOM_TASK rt,
			SYS_DEPARTMENT sd
		WHERE
			rt.CREAT_DEPARTMENT_ID = sd.DEPARTMENT_ID
		AND sd.DEPARTMENT_NUMBER LIKE CONCAT (r.department_num, "%")
		AND rt.distributed_state = 1
		AND rt.STATE = 1
		AND rt.LAUNCH_DATE BETWEEN TO_DATE ("2017-07-05", "yyyy-mm-dd")
		AND (TO_DATE("2017-07-05", "yyyy-mm-dd") + 1)
	) law_user_str
FROM
	random_user_count r
ORDER BY
	r.area_code,
	r.department_num;

可是某一天，这段sql在运行的时候突然报错，提示“字符串连接的结果过长”，网上查询之后才知道，原来用listagg进行拼接，返回的结果是varchar类型，而且有最大长度限制，可以转成club或者截取。。。

后来根据各种链接，找到一个相对靠谱的回答，点击打开链接

改了之后的sql如下：

SELECT
	r.department_id law_dept_id,
	(
		SELECT
-- 			listagg (
-- 				rt.extracted_person_ids,
-- 				","
-- 			) WITHIN GROUP (
-- 				ORDER BY
--  					rt.extracted_person_ids
-- 			)
			xmlagg(xmlparse(content rt.extracted_person_ids||"," wellformed) order by rt.extracted_person_ids).getclobval()
		FROM
			RANDOM_TASK rt,
			SYS_DEPARTMENT sd
		WHERE
			rt.CREAT_DEPARTMENT_ID = sd.DEPARTMENT_ID
		AND sd.DEPARTMENT_NUMBER LIKE CONCAT (r.department_num, "%")
		AND rt.distributed_state = 1
		AND rt.STATE = 1
		AND rt.LAUNCH_DATE BETWEEN TO_DATE ("2017-07-05", "yyyy-mm-dd")
		AND (TO_DATE("2017-07-05", "yyyy-mm-dd") + 1)
	) law_user_str
FROM
	random_user_count r
ORDER BY
	r.area_code,
	r.department_num;

解决问题，结果正常。