MySQL - 如何从表中获取结果，以及在一个查询中有多少个连接项的计数？

Question

I have a query like this:

select display_order , section_name , solution_section_id from solution_sections order by display_order

It is very basic and gets the sections of a particular discussion. It works.

What I want to do is to also display the number of comments in each of the section. So I want to do a join on the comments table and do a count on how many comments there are.

Here is the schema for the other tables:

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    |                |
| guid                  | varchar(50)    | YES  | UNI | NULL    |                |
+-----------------------+----------------+------+-----+---------+----------------+
8 rows in set (0.00 sec)

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    |                |
+---------------------+---------------+------+-----+---------+----------------+

So it would have to be a join on solution_section_id and solution_part (those are the foreign keys even though they are named somewhat inconsistently) where problem_id = some id.

But how would I get the count of the number of returned comments in the suggested_solution_comments table?

Thanks!

Answer 1

SELECT solution_sections.display_order, solution_sections.section_name, solution_sections.solution_section_id, COUNT(suggested_solution_comments.comment_id) FROM solution_sections, suggested_solution_comments GROUP BY solution_sections.solution_section_id

Maybe try something like this? Its been awhile since i touched table joins, and your table naming looks pretty confusing to me.

Answer 2

UPDATED with outer join:

select s.display_order, s.section_name, s.solution_section_id
      ,count(c.comment_id) AS comment_count
  from solution_sections s
  left outer join suggested_solution_comments c ON (c.solution_part = s.solution_section_id)
  group by s.display_order, s.section_name, s.solution_section_id
  order by display_order