SQL: 检测多个相同的条目作为一个批次

Question

用例如下。当我有多个内容相同的条目时，结果应该以某种方式组合在一起，具体取决于确切的数据，除了一些重要的关键。

------------------------------------
| student_id  | subject_id | marks |
------------------------------------
| STD001      | SUB001     | 10    |
| STD001      | SUB002     | 20    |
| STD002      | SUB001     | 10    |
| STD002      | SUB002     | 20    |
| STD003      | SUB001     | 11    |
| STD003      | SUB002     | 20    |
| STD004      | SUB001     | 11    |
| STD004      | SUB002     | 20    |
| STD005      | SUB001     | 11    |
| STD005      | SUB002     | 20    |
| STD005      | SUB003     | 30    |
------------------------------------

预期最终结果

-------------------------------------------------
| subject_id_str       | marks_str | student_id |
-------------------------------------------------
| SUB001_SUB002        | 10_20     | STD001     |
| SUB001_SUB002        | 10_20     | STD002     |
| SUB001_SUB002        | 11_20     | STD003     |
| SUB001_SUB002        | 11_20     | STD004     |
| SUB001_SUB002_SUB003 | 11_20_30  | STD005     |
-------------------------------------------------

或

--------------------------------------------------------
| subject_id_str       | marks_str | student_id_str    |
--------------------------------------------------------
| SUB001_SUB002        | 10_20     | STD001_STD002     |
| SUB001_SUB002        | 11_20     | STD003_STD004     |
| SUB001_SUB002_SUB003 | 11_20_30  | STD005            |
--------------------------------------------------------

More Info: Using MySQL 5.7

Answer 1

您可以使用字符串聚合：

select
    group_concat(subject_id order by subject_id separator '_') as subject_id_str,
    group_concat(marks      order by subject_id separator '_') as marks_str,
    student_id
from mytable
group by student_id

SQL: 检测多个相同的条目作为一个批次

SQL: Detect multiple same entries as a batch

mysql

sql

string

group-by

mysql-5.7