问一条SQL语句

Question

SELECT
  a.logoid,
  a.trainingoid,
  a.employeeoid,
  a.lastDate,
  a.nextDueDate,
  a.fileName
  FROM dbo.OPERATOR_SOP_LOG_ENTRY AS a
  INNER JOIN
  (SELECT
  trainingoid,
  employeeoid,
  MAX(lastDate) AS mdate
  FROM  dbo.OPERATOR_SOP_LOG_ENTRY
  GROUP BY trainingoid, employeeoid) AS b
  ON a.trainingoid = b.trainingoid AND a.lastDate = b.mdate

Answer 1

--取lastdate =按照trainingold和employeeoid分组后最大日期的相应数据SELECT  a.logoid ,
        a.trainingoid ,
        a.employeeoid ,
        a.lastDate ,
        a.nextDueDate ,
        a.fileName
FROM    dbo.OPERATOR_SOP_LOG_ENTRY AS a
        INNER JOIN ( SELECT trainingoid ,
                            employeeoid ,
                            MAX(lastDate) AS mdate
                     FROM   dbo.OPERATOR_SOP_LOG_ENTRY
                     GROUP BY trainingoid ,
                            employeeoid 
                   ) AS b ON a.trainingoid = b.trainingoid  
                             AND a.lastDate = b.mdate

Answer 2

按照trainingold和employeeoid分组是什么意思？

Answer 3

是在trainingoid分组后，再在组内按employeeoid分组？