[英]MAX condition on left outer join
----------
samples
----------
SamplesID
stylenumber
stylename
status
-----------
samples_details
-----------
Samples_Details_ID
SamplesID
CustomerName
date_out
date_returned
updated (timestamp)
status
------------
samples_pictures
------------
SamplesPicID
SamplesID
尝试编写一个查询,它给出了样本中的所有行,samples_pictures中的所有匹配项(如果有)以及samples_details中的最新记录(如果有)。 所以两个左外连接,但只检索最近的记录。
什么不起作用:
SELECT samples.*
, samples_pictures.SamplesPicID
, CustomerName
, date_out
, date_returned
, updated
, samples_details.status as txn_status
FROM samples
LEFT OUTER JOIN
( SELECT Samples_Details_ID
, samples_details.status as txn_status
, MAX(updated) as MaxUpdated
FROM samples_details
GROUP BY Samples_Details_ID
) AS MaxTable
ON MaxTable.SamplesID = samples.SamplesID
LEFT OUTER JOIN samples_pictures
ON samples.SamplesID = samples_pictures.SamplesID
任何帮助将不胜感激!
您的原始查询仍然从samples_details中选择每条记录。
您必须创建一个子选择,以仅筛选出具有最大时间戳的记录,并将其与samples_details表连接,以获取其他列。
SELECT *
FROM samples s
LEFT OUTER JOIN sample_details sd ON sd.SamplesID = s.SamplesID
INNER JOIN (
SELECT SamplesID
, MAX(update) AS Update
FROM samples_details
GROUP BY
SamplesID
) sdm ON sdm.SamplesID = sd.SamplesID
LEFT OUTER JOIN samples_pictures sp ON sp.SamplesID = s.SamplesID
MaxTable
的select语句中没有SamplesID
。 应该:
SELECT samples.*, samples_pictures.SamplesPicID, CustomerName, date_out,
date_returned, updated, samples_details.status as txn_status
FROM samples
LEFT OUTER JOIN (SELECT SamplesID, Samples_Details_ID, samples_details.status as txn_status,
MAX(updated) as MaxUpdated FROM samples_details GROUP BY Samples_Details_ID)
AS MaxTable ON MaxTable.SamplesID = samples.SamplesID
LEFT OUTER JOIN samples_pictures ON samples.SamplesID = samples_pictures.SamplesID
SELECT samples.*
, samples_pictures.SamplesPicID
, CustomerName
, date_out
, date_returned
, updated
, samples_details.status as txn_status
FROM samples
LEFT OUTER JOIN samples_details
ON samples.SamplesID = samples_details.SamplesID
AND samples_details.updated =
( SELECT MAX(updated)
FROM samples_details
WHERE SamplesID = samples.SamplesID)
)
LEFT OUTER JOIN samples_pictures
ON samples.SamplesID = samples_pictures.SamplesID
SELECT samples.*
, samples_pictures.SamplesPicID
, CustomerName
, date_out
, date_returned
, updated
, txn_status
FROM samples
LEFT OUTER JOIN
( SELECT Samples_ID
, status as txn_status
FROM samples_details
INNER JOIN
( SELECT Samples_ID,
Samples_Details_ID
, MAX(updated) as MaxUpdated
FROM samples_details
GROUP BY Samples_ID, Samples_Details_ID
) AS MaxTable
ON MaxTable.Samples_ID = samples.SamplesID
AND MaxTable.Samples_Details_ID = samples.Samples_Details_ID
) AS MaxJoin
LEFT OUTER JOIN samples_pictures
ON samples.SamplesID = samples_pictures.SamplesID
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