creates row_number column that restarts at 1 at the start of a new year or new starting pitcher, which is necessary in order to create a meaningful season-to-date park factor column using the code for creating this season-to-date full park factor column.

create season-to-date league average FIP column

DROP PROCEDURE IF EXISTS starting_pitcher_AL_NL_std_lg_FIP;
CREATE PROCEDURE starting_pitcher_AL_NL_std_lg_FIP()
BEGIN
    DECLARE gdate DATE;
    DECLARE YEARID INT;
    DECLARE lgID CHAR (2);
    DECLARE HR INT;
    DECLARE walks INT;
    DECLARE HitBP INT;
    DECLARE K INT;
    DECLARE in_pit REAL;
    DECLARE conFIP VARCHAR (255);
    DECLARE accum_ip REAL;
    DECLARE accum_walks_a REAL;
    DECLARE accum_HR REAL;
    DECLARE accum_HBP REAL;
    DECLARE accum_K REAL;
    DECLARE stdFIP REAL;
    DECLARE prev_year YEAR(4);
    DECLARE end_of_cursor BOOLEAN;

    DECLARE no_table CONDITION FOR SQLSTATE '42S02';

    DECLARE c1 CURSOR FOR
      SELECT Game_Date, YEAR_ID, lg_ID, lg_HR_a, lg_walks_a, lg_HBP, lg_strike_outs, lg_innings_pitched, cFIP  
        FROM NL_AL_lg_starting_pitcher_stats
        ORDER BY lg_ID, YEAR_ID, Game_Date;
        
    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 gdate, YEARID, lgID, HR, walks, HitBP, K, in_pit, conFIP;
      IF end_of_cursor THEN
        LEAVE fetch_loop;
      END IF;

      -- check control-break conditions
      IF YEAR(gdate) != prev_year THEN
        SET accum_ip := 0.0;
        SET accum_walks_a := 0;
        SET accum_HR := 0;
        SET accum_HBP := 0;
        SET accum_K := 0;
        SET prev_year := YEAR(gdate);
      END IF;

      SET accum_ip := accum_ip + in_pit;
      SET accum_walks_a := accum_walks_a + walks;
      SET accum_HR:= accum_HR + HR;
      SET accum_HBP := accum_HBP + HitBP;
      SET accum_K := accum_K + K;
     
      IF (accum_ip) = 0 OR (in_pit)=0 THEN  
        SET stdFIP := 0;
      ELSE
        SET stdFIP := ((accum_HR*13)+(3*(accum_walks_a+accum_HBP))-(2*accum_K))/accum_ip+conFIP;
      END IF;

      UPDATE NL_AL_lg_starting_pitcher_stats
        SET std_FIP =stdFIP
        WHERE lg_ID = lgID 
          AND YEAR_ID = YEARID
          AND Game_Date = gdate;

    END LOOP;

    CLOSE c1;
  END
$$

DELIMITER ;

creates_row_number_column_that_restarts_at_1

UPDATE starting_pitcher_stats JOIN
       (select starting_pitcher_stats.*,
               (@rn := if(@sy = concat_ws(':', Starting_Pitcher, YEAR_ID), @rn + 1,
                          if(@sy := concat_ws(':', Starting_Pitcher, YEAR_ID), 1, 1)
                         )
               ) as rn
        from starting_pitcher_stats CROSS JOIN
             (select @rn := 0, @sy := '') params
        order by Starting_Pitcher, YEAR_ID, Game_Date, Game_Number
       ) sp2
       on sp2.Starting_Pitcher = starting_pitcher_stats.Starting_Pitcher AND
          sp2.YEAR_ID = starting_pitcher_stats.YEAR_ID AND
          sp2.Game_Date = starting_pitcher_stats.Game_Date AND
          sp2.Game_Number=starting_pitcher_stats.Game_Number
    set starting_pitcher_stats.row_number = sp2.rn;