mysql - 将内部连接转换为左侧连接

Question

我有一个 rake 文件，上面有这段代码。 .

   if circle[:conference2_total_channels].present?
                conf = Confbridge.find(:all, :conditions => ["confbridges.cid = ?",circle.circle_number],
                :joins => [:confbridge_participants],
                :select => 'confbridges.id, confbridges.confno, confbridges.max_member, (confbridges.max_member - 5) AS additional , (confbridges.max_member - IFNULL(confbridge_participants.active,0)) AS vacant')

            end

代码的返回是

SELECT confbridges.id, confbridges.confno, confbridges.max_member, (confbridges.max_member - 5) AS additional , (confbridges.max_member - IFNULL(confbridge_participants.active,0)) AS vacant FROM `confbridges` **INNER JOIN** `confbridge_participants` ON `confbridge_participants`.`confbridge_id` = `confbridges`.`id` WHERE (confbridges.cid = '0090000092')

它是INNER JOIN

如何将其更改为LEFT JOIN

像这样

SELECT confbridges.id, confbridges.confno, confbridges.max_member, (confbridges.max_member - 5) AS additional , (confbridges.max_member - IFNULL(confbridge_participants.active,0)) AS vacant FROM `confbridges` **LEFT JOIN** `confbridge_participants` ON `confbridge_participants`.`confbridge_id` = `confbridges`.`id` WHERE (confbridges.cid = '0090000092')

谢谢 :)

Answer 1

我会这样写:

Confbridge.where("confbridges.cid = ?",circle.circle_number)
  .joins("LEFT JOIN confbridge_participants 
         ON confbridge_participants.confbridge_id = confbridges.id")
  .select(...your select statement)