----------
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)以及来自samples_details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！
最佳答案
您的原始查询仍然从samples_details中选择每条记录.
原文链接：https://www.f2er.com/mysql/432998.html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