MySQL 查询其他表的 2 个 COUNT() 并带有 where 条件

Question

我有一个名为“运动”的表，其中包含运动列表的列表，其他称为“季节”的表，其中包含特定运动的季节以及包含特定运动和季节的比赛的比赛。

我需要一个 MySQL 查询来打印体育项目列表，以及每个体育项目有多少个赛季和比赛。我的表格结构:

运动

+--------------------+------------------+------+-----+---------+----------------+
| Field              | Type             | Null | Key | Default | Extra          |
+--------------------+------------------+------+-----+---------+----------------+
| id                 | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| name               | varchar(32)      | NO   |     | NULL    |                |
| slug               | varchar(45)      | NO   |     | NULL    |                |
| description        | varchar(128)     | NO   |     | NULL    |                |
+--------------------+------------------+------+-----+---------+----------------+

季节

+--------------------+------------------+------+-----+---------+----------------+
| Field              | Type             | Null | Key | Default | Extra          |
+--------------------+------------------+------+-----+---------+----------------+
| id                 | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| id_sport           | int(10) unsigned | NO   | MUL | NULL    |                |
| name               | varchar(32)      | NO   |     | NULL    |                |
| slug               | varchar(32)      | NO   |     | NULL    |                |
+--------------------+------------------+------+-----+---------+----------------+

比赛

+--------------------+------------------+------+-----+---------+----------------+
| Field              | Type             | Null | Key | Default | Extra          |
+--------------------+------------------+------+-----+---------+----------------+
| id                 | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| id_season          | int(10) unsigned | NO   | MUL | NULL    |                |
| name               | varchar(32)      | NO   |     | NULL    |                |
| slug               | varchar(64)      | NO   |     | NULL    |                |
| description        | varchar(128)     | YES  |     | NULL    |                |
+--------------------+------------------+------+-----+---------+----------------+

我的查询结果需要包含:sports.*、total_seasons(季节的总和，其中seasons.id_sport=sports.id)和total_competitions(比赛的总和，其中competitions.id_season=seasons.id AND seasons.id_sport=sports .id)。

提前谢谢您!

Answer 1

使用左连接代替内连接

select
  sports.id,
  sports.name,
  sports.slug,
  sports.description,
  ifnull(count( distinct seasons.id ), 0) as DistinctSeasons,
  ifnull(count( distinct competitions.id ), 0) as TotalCompetitions
from 
  sports
  left join seasons on sports.id=seasons.id_sport
  left join competitions on seasons.id = competitions.id_season
group by
  sports.id;