找到父节点下的所有子节点（包括子节点）

CREATE TABLE `tab_menu` (
  `MU_ID` int(10) NOT NULL AUTO_INCREMENT COMMENT ‘主键‘,
  `MU_NAME` varchar(255) NOT NULL COMMENT ‘菜单名‘,
  `MU_CODE` varchar(100) DEFAULT NULL COMMENT ‘菜单编码‘,
  `MU_CHAIN_NAME` varchar(255) NOT NULL COMMENT ‘菜单全名‘,
  `MU_PARENT_ID` int(10) NOT NULL COMMENT ‘上级菜单ID‘,
  `MU_URL` varchar(255) NOT NULL COMMENT ‘菜单URL‘,
  `STATUS` smallint(1) NOT NULL DEFAULT ‘1‘ COMMENT ‘状态;0：未启用 1:已启用,默认为1‘,
  `MU_ELEMENT_TYPE` varchar(40) NOT NULL COMMENT ‘所属元素类型‘,
  `MU_SCOPE` varchar(20) NOT NULL DEFAULT ‘common‘ COMMENT ‘菜单作用范围;‘,
  `CREATE_USER_ID` int(11) NOT NULL COMMENT ‘创建用户ID‘,
  `CREATE_TIME` datetime NOT NULL COMMENT ‘创建时间‘,
  `UPDATE_USER_ID` int(11) DEFAULT NULL COMMENT ‘修改用户ID‘,
  `UPDATE_TIME` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT ‘修改时间‘,
  `VERSION_NUMBER` int(11) NOT NULL DEFAULT ‘0‘ COMMENT ‘版本号:新增资料为 0，每次修改加 1‘,
  PRIMARY KEY (`MU_ID`),
  KEY `idx_menu_url` (`MU_URL`)
) ENGINE=InnoDB AUTO_INCREMENT=2040101 DEFAULT CHARSET=utf8 COMMENT=‘菜单‘;

CREATE DEFINER=`ggs`@`%` FUNCTION `pkg_pm_fun_get_children_branch`(menu_id int(10)) RETURNS text CHARSET utf8 COLLATE utf8_bin
begin
    declare menu_ids TEXT;
    declare tmp_menu_ids text;
    set tmp_menu_ids =‘$‘;
    set menu_ids = cast(menu_id as char);
    while menu_ids is not null do
        set tmp_menu_ids = concat(tmp_menu_ids,‘,‘,menu_ids);
        select group_concat(mu_id) into menu_ids from tab_menu where find_in_set(mu_parent_id,menu_ids) > 0;
    end while;
    return tmp_menu_ids;
end