試圖瞭解和優化mysql查詢

Question

我們在下面有一個查詢。它在根據日期搜索最新培訓的地方工作得很好。我想了解爲什麼我們要把B1.driverTrainingDate < B2.driverTrainingDate而不是其他方式，而且B2.driverID IS NULL。是否有任何其他選項來改善此查詢？

SELECT driver.driverID,b.driverTrainingDate 
FROM driver 
      LEFT JOIN (
    SELECT B1.* 
         FROM dTraining AS B1 
          LEFT JOIN dTraining AS B2 
            ON B1.driverID = B2.driverID 
             AND B1.cTrainingID = B2.cTrainingID 
             AND B1.driverTrainingDate< B2.driverTrainingDate 
         WHERE B1.cID=".$cTID." And B2.driverID IS NULL) as b 
ON (driver.driverID= b.driverID) 

Answer 1

我認爲這是打算返回剛好在完整記錄之前但具有空驅動ID的訓練日期。

'相反的方式'意味着後面的...如果該數據模式甚至存在。