尝试使用 MySQL 创建具有同一 table 中另一列的季至今平均值的列

Question

我正在努力确定 MySQL 代码以在我的 table "starting_pitcher_stats" 中创建一个列（平均 park_factor），我想包含另一列 (park_factor) 中值的季内平均值。我希望这个赛季内平均值按投手和日期分组。

理想情况下，table 看起来像这样：

    pitcher     park_fac   avg_park_fac       date
    aased001    94         94           1977-07-31
    aased001    100        97           1977-08-06
    aased001    108        100.666      1977-08-11
    aased001    108        102.5        1977-08-16
    aased001    96         101.2        1977-08-21
    aased001    108        102.33       1977-08-26
    aased001    108        103.14       1977-08-31
    aased001    104        103.25       1977-09-05
    aased001    108        103.77       1977-09-10
    aased001    92         102.6        1977-09-16
    aased001    106        102.9        1977-09-22
    aased001    108        103.33       1977-09-27

我使用的代码是：

SELECT Starting_Pitcher, full_park_factor, AVG(full_park_factor), Game_Date
FROM starting_pitcher_stats 
GROUP BY Starting_Pitcher, Game_Date, Game_Number

...结果 table 的样本如下所示：

pitcher     park_fac   avg_park_fac  date
aased001    94         94.0000      1977-07-31
aased001    100        100.0000     1977-08-06
aased001    108        108.0000     1977-08-11
aased001    108        108.0000     1977-08-16
aased001    96         96.0000      1977-08-21
aased001    108        108.0000     1977-08-26
aased001    108        108.0000     1977-08-31
aased001    104        104.0000     1977-09-05
aased001    108        108.0000     1977-09-10
aased001    92         92.0000      1977-09-16
aased001    106        106.0000     1977-09-22
aased001    108        108.0000     1977-09-27

有人可以帮忙吗？

在此先感谢您的帮助。李

Answer 1

您需要加入您的 table 之前所有来自同一 table 的同一投手的结果。

我不太确定您是如何定义季节的，但假设它是按日历年定义的，则以下查询会产生所需的输出。

SELECT
    a.Starting_Pitcher, a.full_park_factor,
    AVG(b.full_park_factor), a.Game_Date, a.Game_Number
FROM starting_pitcher_stats a
INNER JOIN starting_pitcher_stats b
    ON a.Starting_Pitcher = b.Starting_Pitcher
    AND (b.Game_Date < a.Game_Date OR
         (b.Game_Date = a.Game_Date AND b.Game_Number <= a.Game_Number))
    AND YEAR(b.Game_Date) = YEAR(a.Game_Date)
GROUP BY a.Starting_Pitcher, a.Game_Date, a.Game_Number;

您似乎想用此计算结果更新 table 中的一列。这可以通过使用触发器进行实时更新来实现，该触发器会在您插入或更新现有数据或使用视图时更新列。

CREATE VIEW starting_pitcher_stats_with_average AS
SELECT
    a.Starting_Pitcher, a.full_park_factor,
    AVG(b.full_park_factor), a.Game_Date, a.Game_Number
FROM starting_pitcher_stats a
INNER JOIN starting_pitcher_stats b
    ON a.Starting_Pitcher = b.Starting_Pitcher
    AND (b.Game_Date < a.Game_Date OR
         (b.Game_Date = a.Game_Date AND b.Game_Number <= a.Game_Number))
    AND YEAR(b.Game_Date) = YEAR(a.Game_Date)
GROUP BY a.Starting_Pitcher, a.Game_Date, a.Game_Number;

在您自己的回答中，您创建了一个程序来一次性更新 table 中所有记录的平均列，因此您可能不希望在插入数据时更新列，但是只需能够按需添加所有行的平均值。在这种情况下，您可以编写一个 UPDATE 语句，其中包含上面的 SELECT 查询作为子查询。因为 MySQL 不能对 UPDATE 和子查询使用相同的 table，所以您必须将子查询包装在另一个 SELECT 中，以便 MySQL 生成临时 table 根据您的结果。

UPDATE starting_pitcher_stats c
SET c.std_F_parkfactor = (
    SELECT d.std_F_parkfactor FROM (
        SELECT
            a.Starting_Pitcher,
            AVG(b.full_park_factor) std_F_parkfactor,
            a.Game_Date, a.Game_Number
        FROM starting_pitcher_stats a
        INNER JOIN starting_pitcher_stats b
            ON a.Starting_Pitcher = b.Starting_Pitcher
            AND (b.Game_Date < a.Game_Date OR
                 (b.Game_Date = a.Game_Date
                  AND b.Game_Number <= a.Game_Number))
            AND YEAR(b.Game_Date) = YEAR(a.Game_Date)
        GROUP BY a.Starting_Pitcher, a.Game_Date, a.Game_Number
    ) d
    WHERE c.Starting_Pitcher = d.Starting_Pitcher
    AND c.Game_Date = d.Game_Date
    AND c.Game_Number = d.Game_Number
);

Answer 2

更新：这是一种将给定季节的季节至今（季节内）公园因子平均值存储在列中的方法，在这种情况下，它是同一列中另一列值的平均值 table 使用存储过程。它基本上通过除以 row_number 来计算平均值，row_number 对应于在计算此变量时循环的值的行数。如果您已经收集了想要一次性更新或很少更新的数据，则此方法有效，但正如 Matt Raines 所暗示的那样，可能必须比他建议的方法运行更频繁。如果 table 至少每天更新一次连续几天比赛结果的数据，我认为使用他的方法会减少劳动强度。请告诉我可以消除的内容：

DROP PROCEDURE IF EXISTS std_park_factor_avg;
DELIMITER $$
CREATE PROCEDURE std_park_factor_avg()
BEGIN
    DECLARE pit_id CHAR(10);
    DECLARE lgID CHAR (2); 
    DECLARE YEARID INT;
    DECLARE gdate DATE;
    DECLARE seq INT;
    DECLARE F_park_factor INT;
    DECLARE RNUMBER INT;
    DECLARE accum_F_parkfactor REAL;
    DECLARE accum_row_number INT;
    DECLARE accum_avg_F_parkfactor REAL;
    DECLARE prev_year YEAR(4);
    DECLARE end_of_cursor BOOLEAN;

    DECLARE no_table CONDITION FOR SQLSTATE '42S02';

    DECLARE c1 CURSOR FOR
      SELECT Starting_Pitcher, lg_ID, YEAR_ID, Game_Date, Game_Number, full_park_factor, ROW_NUMBER 
        FROM starting_pitcher_stats
        GROUP BY Starting_Pitcher, lg_ID, YEAR_ID, Game_Date, Game_Number;

    DECLARE CONTINUE HANDLER FOR NOT FOUND
      SET end_of_cursor := TRUE;

    SET end_of_cursor := FALSE;  -- reset
    SET prev_year := 0;          -- reset control-break

    OPEN c1;

    fetch_loop: LOOP
      FETCH c1 INTO pit_id, lgID, YEARID, gdate,seq, F_park_factor, RNUMBER;
      IF end_of_cursor THEN
        LEAVE fetch_loop;
      END IF;

      -- check control-break conditions
      IF YEAR(gdate) != prev_year THEN
       SET accum_F_parkfactor := 0.0;
       SET RNUMBER:= 1.0;
       SET accum_avg_F_parkfactor := 0.0;
        SET prev_year := YEAR(gdate);
      END IF;

     SET accum_F_parkfactor := accum_F_parkfactor + F_park_factor;
     SET accum_avg_F_parkfactor := accum_F_parkfactor/RNUMBER;

      UPDATE starting_pitcher_stats
        SET std_F_parkfactor =accum_avg_F_parkfactor
        WHERE Starting_Pitcher = pit_id
          AND lg_ID = lgID 
          AND YEAR_ID = YEARID
          AND Game_Date = gdate
          AND Game_Number = seq;

    END LOOP;
    CLOSE c1;
  END
$$

DELIMITER ;

尝试使用 MySQL 创建具有同一 table 中另一列的季至今平均值的列

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