mysql连接和计数

Question

以某种方式创建我想要的查询不成功。

DB与位置有关，有以下相关的表

• t_location - 包含的位置列表字段t_location_zipcode和t_location_id_location
• t_zipcodecity - 加入表格t_zipcodecity_zipcode t_zipcodecity_id_city
• t_city - 包含t_city_id_city
的城市列表
• t_citystate - join table，t_citystate_id_city，t_citystate_id_state
• t_state - 包含t_state_id_state
的州名单

最初，我尝试使用此查询获取包含位置的状态列表：

SELECT DISTINCT `t_state_id_state`
      , `t_state_name_full` 
  FROM (`t_state`) 
LEFT JOIN `t_citystate` ON `t_state_id_state` = `t_citystate_id_state` 
LEFT JOIN `t_city` ON `t_citystate_id_state` = `t_city_id_city` 
LEFT JOIN `t_zipcodecity` ON `t_city_id_city` = `t_zipcodecity_id_city` 
LEFT JOIN `t_location` ON `t_zipcodecity_zipcode` = `t_location_zipcode` 
ORDER BY `t_state_name_full` asc ­

工作正常。

现在我需要/想要的是我失败的是获得每个州的位置数量。我不知道是否可以在这一个查询中完成，或者我是否需要另一个查询，无论哪种方式我都需要帮助！

Answer 1

您可以使用计数和分组。像这样：

SELECT DISTINCT `t_state_id_state`
          , `t_state_name_full`
          , COUNT(*) 
      FROM (`t_state`) 
 LEFT JOIN `t_citystate` ON `t_state_id_state` = `t_citystate_id_state` 
 LEFT JOIN `t_city` ON `t_citystate_id_state` = `t_city_id_city` 
 LEFT JOIN `t_zipcodecity` ON `t_city_id_city` = `t_zipcodecity_id_city` 
 LEFT JOIN `t_location` ON `t_zipcodecity_zipcode` = `t_location_zipcode` 
  GROUP BY `t_state_id_state` , `t_state_name_full`
  ORDER BY `t_state_name_full` asc

Answer 2

SELECT  t_state_id_state
      , t_state_name_full 
      , COUNT(DISTINCT t_location_id_location) AS locations_number

  FROM 
        t_state
    LEFT JOIN 
        t_citystate   ON t_state_id_state = t_citystate_id_state 
    LEFT JOIN 
        t_city   ON t_citystate_id_state = t_city_id_city 
    LEFT JOIN 
        t_zipcodecity   ON t_city_id_city = t_zipcodecity_id_city 
    LEFT JOIN 
        t_location   ON t_zipcodecity_zipcode = t_location_zipcode 

  GROUP BY t_state_id_state 

  ORDER BY t_state_name_full ASC ­

Answer 3

好吧，那看起来很好，我的左连接坏了，我最初试图获得所有状态，这就是我使用它们的原因。但我改变它以使用内连接

SELECT  t_state_id_state,
t_state_name_full,
COUNT(DISTINCT t_location_id_location) AS locations_number
FROM t_state
INNER JOIN t_citystate ON t_citystate_id_state = t_state_id_state 
INNER JOIN t_city ON t_city_id_city = t_citystate_id_city 
INNER JOIN t_zipcodecity ON t_zipcodecity_id_city = t_city_id_city 
INNER JOIN t_location ON t_location_zipcode = t_zipcodecity_zipcode 
GROUP BY t_state_id_state 
ORDER BY t_state_name_full ASC 

然后我的结果看起来很棒！