MYSQL：左只加入第一行或选择不同

Question

我试图做几个表上的左连接。但是，它显示了所有左连接表结果。主表是'a'，但它显示重复的id，因为它的id在其他表上多次存在。我怎样才能选择其他表格上的第一行？或者在表格'a'上选择不同的结果？这里是我的SQL

SELECT a.adsId, a.adsName, a.adsUrl, a.sourceFileName, c.userName, d.preferenceId, e.ppv FROM y5ads_new.ads_source a 
       INNER JOIN y5ads_new.campaign b ON a.campaignId=b.campaignId 
       INNER JOIN y5ads_new.system_member c ON b.createdBy=c.memberId 
       INNER JOIN y5ads_new.ads_preference d ON a.adsId=d.adsId 
       INNER JOIN y5ads_new.ads_rates e ON a.adsId=e.adsId 
       WHERE a.status='2' AND a.deleted='False' AND CURDATE() BETWEEN a.startDate and a.endDate 
       AND b.status='2' AND b.deleted='False' AND CURDATE() BETWEEN b.startDate and b.endDate 
       AND d.deleted='False' AND CURDATE() BETWEEN d.startDate and d.endDate 
       AND e.is_active='1' AND CURDATE() BETWEEN e.startDate and e.endDate 
       ORDER BY a.adsId DESC, d.preferenceId DESC, e.id DESC 

Answer 1

让你的ID不同，并使用LEFT JOIN：

SELECT a.adsId, a.adsName, a.adsUrl, a.sourceFileName, c.userName, d.preferenceId, e.ppv 
FROM y5ads_new.ads_source AS a 
LEFT JOIN (SELECT DISTINCT campaignId as campaignId FROM y5ads_new.campaign) AS b 
ON a.campaignId=b.campaignId 
LEFT JOIN (SELECT DISTINCT memberId AS memberId, userName FROM y5ads_new.system_member) AS c 
ON b.createdBy=c.memberId 
LEFT JOIN (SELECT DISTINCT adsId AS adsId, preferenceId FROM y5ads_new.ads_preference) AS d 
ON a.adsId=d.adsId 
LEFT JOIN (SELECT DISTINCT adsId AS adsId, ppv FROM y5ads_new.ads_rates) AS e 
ON a.adsId=e.adsId 
WHERE ...