我有以下查询，给我有关StatsStrategySessions表的第二个JOIN / COUNT的问题：
SELECT
fa.Id
, CAST(fa.StatDate AS DATE)
, COUNT(sa.CreatedDateTime) AS 'TotalApplications'
, COUNT(ss.CreatedDateTime) AS 'TotalStrategySessions'
FROM StatsFacebookAds fa
LEFT JOIN StatsApplications sa
ON CAST(fa.StatDate AS DATE) = CAST(sa.CreatedDateTime AS DATE)
AND sa.LeadSourceId = 1
LEFT JOIN StatsStrategySessions ss
ON CAST(fa.StatDate AS DATE) = CAST(ss.CreatedDateTime AS DATE)
AND ss.LeadSourceId = 1
GROUP BY
fa.Id
, fa.StatDate
它返回的数量应该是它的两倍...
它返回...
Id TotalApplications TotalStrategySessions
----------- ---------- ----------------- ---------------------
1 2019-12-02 1 1
2 2019-12-03 0 0
3 2019-12-04 0 0
4 2019-12-05 4 4
第二个JOIN / COUNT倍增至4，而不是原来的2。
当我在没有第二个JOIN / COUNT的情况下运行代码时，它会按预期返回。
代码按预期运行。
SELECT
fa.Id
, CAST(fa.StatDate AS DATE)
, COUNT(sa.CreatedDateTime) AS 'TotalApplications'
FROM StatsFacebookAds fa
LEFT JOIN StatsApplications sa
ON CAST(fa.StatDate AS DATE) = CAST(sa.CreatedDateTime AS DATE)
AND sa.LeadSourceId = 1
GROUP BY
fa.Id
, fa.StatDate
它返回我期望的...
Id TotalApplications
----------- ---------- -----------------
1 2019-12-02 1
2 2019-12-03 0
3 2019-12-04 0
4 2019-12-05 2
但是，一旦我加入第二张表，数字就不是我要显示的数字了。
自从我写了tsql以来已经有一段时间了，希望我能在它上面留一些...
感谢您的帮助！
答案 0 :(得分：0)
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表上使用不同的计数：
StatsApplications这里的概念是，SELECT
fa.Id,
CAST(fa.StatDate AS DATE),
COUNT(DISTINCT sa.CreatedDateTime) AS [TotalApplications], -- change is here
COUNT(ss.CreatedDateTime) AS [TotalStrategySessions]
FROM StatsFacebookAds fa
LEFT JOIN StatsApplications sa
ON CAST(fa.StatDate AS DATE) = CAST(sa.CreatedDateTime AS DATE) AND
sa.LeadSourceId = 1
LEFT JOIN StatsStrategySessions ss
ON CAST(fa.StatDate AS DATE) = CAST(ss.CreatedDateTime AS DATE) AND
ss.LeadSourceId = 1
GROUP BY
fa.Id,
fa.StatDate;
表的第二个附加连接冒着复制StatsStrategySessions表中所有记录的风险，因为后面的每个记录可能都连接到前一个记录中的多个记录。但是，通过采用非重复计数，我们可以消除重复计数。
如果您不喜欢这种方法，那么处理此问题的另一种方法是在两个表上联接一个子查询，该子查询分别查找计数，然后联接回StatsApplications。