MAX条件加入

Question

---------- 
samples 
---------- 
SamplesID 
stylenumber 
stylename 
status 

----------- 
samples_details 
----------- 
Samples_Details_ID 
SamplesID 
CustomerName 
date_out 
date_returned 
updated (timestamp) 
status 

------------ 
samples_pictures 
------------ 
SamplesPicID 
SamplesID 

想写一个查询，让我从样本中的所有行，从samples_pictures所有比赛（如果有的话），并从samples_details最近的记录（如果有的话）。所以两个左外连接，但只检索最近的记录。

什么是不工作：

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 

任何援助将不胜感激！

Answer 1

在你的select语句中没有SamplesIDMaxTable。应该是：

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 

Answer 2

原始查询仍然选择从samples_details每个记录。

您必须创建一个子查询来筛选出具有最大时间戳记的记录，并将其与samples_details表加回来以获取其他列。

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 

Answer 3

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 

Answer 4

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