mysql GROUP_CONCAT使用

SELECT parent_id AS parent_id, GROUP_CONCAT(DISTINCT child_id ORDER BY child_id) AS child_id_list 
FROM `group_c`
group by parent_id 
ORDER BY parent_id; 

SELECT parent_id AS parent_id, GROUP_CONCAT(DISTINCT child_id ORDER BY child_id separator '|') AS child_id_list 
FROM `group_c`
group by parent_id 
ORDER BY parent_id;