mysql - SQL 查询不会为连接中的每个匹配项返回多行

Question

我有 2 张 table :

mysql> describe solution_sections;
+---------------------+---------------+------+-----+---------+----------------+
| Field               | Type          | Null | Key | Default | Extra          |
+---------------------+---------------+------+-----+---------+----------------+
| solution_section_id | int(10)       | NO   | PRI | NULL    | auto_increment |
| display_order       | int(10)       | NO   |     | NULL    |                |
| section_name        | varchar(1000) | YES  |     | NULL    |                |
+---------------------+---------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

mysql> describe suggested_solution_comments;

+-----------------------+----------------+------+-----+---------+----------------+
| Field                 | Type           | Null | Key | Default | Extra          |
+-----------------------+----------------+------+-----+---------+----------------+
| comment_id            | int(10)        | NO   | PRI | NULL    | auto_increment |
| problem_id            | int(10)        | NO   |     | NULL    |                |
| suggested_solution_id | int(10)        | NO   |     | NULL    |                |
| commenter_id          | int(10)        | NO   |     | NULL    |                |
| comment               | varchar(10000) | YES  |     | NULL    |                |
| solution_part         | int(3)         | NO   |     | NULL    |                |
| date                  | date           | NO   |     | NULL    |                |
+-----------------------+----------------+------+-----+---------+----------------+

我想要做的是显示solution_sections表中的section_name列表，以及建议_solution_comments表中每个section_name的n个匹配项。因此，对于每个部分名称，查询应该获取与其关联的 suggest_solution_comments 列表。

这些表通过 suggest_solution_comments.solution_part 和 Solution_sections.solution_section_id 链接

这是我到目前为止正在尝试的:

select section_name , comment , solution_part , display_order from solution_sections 
    left join suggested_solution_comments on 
    solution_sections.solution_section_id = suggested_solution_comments.solution_part   
    where suggested_solution_id = 188 OR suggested_solution_id IS NULL
    group by display_order;

问题是查询获取了section_name 的列表，以及每个section_name 一个匹配的注释，但不超过一个注释。知道为什么它没有得到所有相关的评论吗？

谢谢!!

Answer 1

GROUP BY 可能会解释您在没有它的情况下所看到的尝试(根据评论进行更新)

select section_name , comment , solution_part , display_order 
from solution_sections 
left join suggested_solution_comments on 
solution_sections.solution_section_id = suggested_solution_comments.solution_part   
where suggested_solution_id = 188 OR suggested_solution_id IS NULL
order by display_order;

一些评论:

您的数据模型似乎有点奇怪...例如 solution_part 是 int(3) 并链接到 solution_section_id 这是转是一个autoincrement int(10)？