MySQL LEFT JOIN与GROUP BY和WHERe IN（子查询）

SELECt a.date, COUNT(b.campaignid) totalStat
FROM campaigndata a
LEFT JOIN campaignfilter b
ON a.campaignid = b.campaignid AND
b.campaigntype = 1
GROUP BY a.date

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• SQL连接的可视表示

更新1

SELECt  a.date,         COALESCE(b.totals,0) totalsFROM    demo_calendar a        LEFT JOIN        ( SELECt  a.date, SUM(impressions) totals FROM    demo_campaigndata a         INNER JOIN demo_campaignfilter b  ON a.campaignid = b.campaignid WHERe   b.campaigntype = 1 GROUP   BY a.date        ) b ON a.date = b.date