Question

以下是我将表与给定EMPLOYE_ID的最新记录连接起来的问题，我想知道是否有更有效/更快的方法来检索最近的记录，什么是最好的方法？

SELECT * FROM EMPLOYEE
WHERE NOT EXISTS (
                       SELECT 1
                       FROM EMPLOYEE D
                       JOIN EMPLOYEE_HISTORY E
                               ON  E.EMPLOYEE_ID = D.EMPLOYEE_ID
                               AND E.CREATE_DATE IN (SELECT MAX(CREATE_DATE) 
                                                   FROM EMPLOYEE_HISTORY 
                                                   WHERE EMPLOYEE_ID = D.EMPLOYEE_ID)
                  )

当我将解释计划与以下查询进行比较时，以下方法似乎更加昂贵。

SELECT *
FROM EMPLOYEE
WHERE NOT EXISTS 
    (SELECT 1
       FROM EMPLOYEE D
       JOIN   (
            SELECT  E.*
            FROM EMPLOYEE_HISTORY E 
            INNER JOIN  (
                            SELECT  EMPLOYEE_ID
                                ,   MAX(CREATE_DATE) max_date
                            FROM EMPLOYEE_HISTORY E2 
                            GROUP BY EMPLOYEE_ID
                            ) EE
                            ON  EE.EMPLOYEE_ID = E.EMPLOYEE_ID
                            AND EE.max_date = E.CREATE_DATE
              ) A
       ON  A.EMPLOYEE_ID = D.EMPLOYEE_ID 
       AND ROWNUM = 1)

那么这是否意味着它确实更好？

CREATE_DATE没有索引，但是PK在CREATE_DATE EMPLOYEE_ID

Answer 1

I would write the query using = rather than IN:

 SELECT 1
 FROM EMPLOYEE E JOIN
      EMPLOYEE_HISTORY EH
      ON EH.EMPLOYEE_ID = E.EMPLOYEE_ID AND
         EH.CREATE_DATE = (SELECT MAX(EH2.CREATE_DATE) 
                           FROM EMPLOYEE_HISTORY EH2
                           WHERE EH2.EMPLOYEE_ID = EH.EMPLOYEE_ID
                          );

IN is more general than = for the comparison.

Your primary key index should be used for the subquery, which should make it pretty fast.

Assuming that you actually do want to return actual columns, then I'm not sure if there is a way to make this faster.

If you really are selecting only 1, then forget the most recent record and just use EXISTS:

 SELECT 1
 FROM EMPLOYEE E
 WHERE EXISTS (SELECT 1
               FROM EMPLOYEE_HISTORY EH2
               WHERE EH2.EMPLOYEE_ID = E.EMPLOYEE_ID
              );

The only additional condition your query checks for is that CREATE_DATE is not NULL, but I'm guessing that is always true anyway.

Answer 2

Use the RANK (or DENSE_RANK or ROW_NUMBER) analytic function:

SELECT 1
FROM EMPLOYEE E
JOIN   (
  SELECT *
  FROM   (
    SELECT  H.*,
            RANK() OVER ( PARTITION BY EMPLOYEE_ID ORDER BY CREATE_DATE DESC ) AS rnk
    FROM    EMPLOYEE_HISTORY H
  )
  WHERE rnk = 1
) H
ON  H.EMPLOYEE_ID = E.EMPLOYEE_ID

Answer 3

If the CREATE_DATE of the EMPLOYEE must be after the maximum CREATE_DATE for that EMPLOYEE_ID in EMPLOYEE_HISTORY?

Then for that EMPLOYEE_ID, there doesn't exist an equal or higher CREATE_DATE in EMPLOYEE_HISTORY.

SELECT * 
FROM EMPLOYEE Emp
WHERE NOT EXISTS (
    SELECT 1
    FROM EMPLOYEE_HISTORY Hist
    WHERE Hist.EMPLOYEE_ID = Emp.EMPLOYEE_ID
      AND Hist.CREATE_DATE >= Emp.CREATE_DATE
)

Test here

Oracle 12c-联接最大日期记录的有效方法

3 个答案: