查询没有没有某种类型的班级的学生，可通过多声部过滤

mec-biz/src/main/java/com/ym/mec/biz/service/impl/ClassGroupStudentMapperServiceImpl.java

@@ -403,6 +403,9 @@ public class ClassGroupStudentMapperServiceImpl extends BaseServiceImpl<Long, Cl
             if (studentIds.size() < 3 && musicGroup.getStatus().equals(MusicGroupStatusEnum.PREPARE)) {
                 throw new BizException("线上基础技能班人数不能小于3人");
             }
+            if (studentIds.size() < 3 && !musicGroup.getStatus().equals(MusicGroupStatusEnum.PREPARE) && oldNormalStudentIds.size() <=0) {
+                throw new BizException("线上基础技能班人数不能小于3人");
+            }
             if (studentIds.size() > 6) {
                 throw new BizException("线上基础技能班人数不能大于6人");
             }