修改m_library结构，student_id,group_number,task_number三个字段组成唯一性索引

stmms-web/src/main/webapp/sql/stmms_ft.sql

@@ -341,8 +341,8 @@ CREATE TABLE `m_library` (
   `header_score_list` varchar(255) DEFAULT NULL COMMENT '科组长给分明细',
   `header_time` datetime DEFAULT NULL COMMENT '科组长评卷时间',
   PRIMARY KEY (`id`),
-  UNIQUE KEY `index1` (`exam_id`,`subject_code`,`group_number`,`status`),
-  KEY `index2` (`student_id`,`group_number`),
+  KEY `index1` (`exam_id`,`subject_code`,`group_number`,`status`),
+  UNIQUE KEY `index2` (`student_id`,`group_number`,`task_number`),
   KEY `index3` (`marker_id`,`status`,`marker_time`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='评卷任务表';