[Every derived table must have its own alias] 在编写mybatis mapper文件时出现的sql错误

直译：每个派生类出现的表必须有一个自己的别名

出现问题场景：多个表关联，且需要查询一个中间表，在编写mybatis mapper文件时出现的错误

解决问题后的sql：

@Select(" select * from ( select source.*,target.dept_name as userDept, target1.dict_name as sexName, group_concat(t2.role_name) as roleNames" +
        " from sys_user source " +
        " left join sys_dept target on source.dept_id = target.id and target.is_delete=0 " +
        " left join sys_dict target1 on source.sex = target1.code and target1.parent_code = 'sex' " +
        " left join sys_role_user t1 on source.id = t1.user_id " +
        " left join sys_role t2 on t1.role_id = t2.id " +
        " group by source.id,userDept,sexName ) as t3" +
        " ${ew.customSqlSegment}")