Question

我有以下查询：

SET @year1 = 2011;

select  B.YearID, sum(B.ab), sum(B.h), sum(B.h)/ sum(B.ab)
    From Batting B join Pitching P 
    on (P.playerID = B.playerID and B.yearID = P.yearid and B.ab > 0 ) 

        where  B.yearid = @year1

这可以很好地检索一年的结果。但是我可以在mySQL上使用循环来执行查询并查看每年的结果吗？

此代码不起作用并产生语法错误：

SET @year1 = 2011;

While @year1 <= 2014 DO

SET @year1 = @year1 + 1;

select  B.YearID, sum(B.ab), sum(B.h), sum(B.h)/ sum(B.ab)
    From Batting B join Pitching P 
    on (P.playerID = B.playerID and B.yearID = P.yearid and B.ab > 0 ) 

        where  B.yearid = @year1;
End While

我可以在MySQL中编写查询，还是必须使用PHP等语言？

Answer 1

最简单的方法是使用group by：

select  B.YearID, sum(B.ab), sum(B.h), sum(B.h)/ sum(B.ab)
From Batting B join Pitching P 
on (P.playerID = B.playerID and B.yearID = P.yearid and B.ab > 0 ) 
where b.yearid>=2011 and b.yearid<=2014
group by B.yearid;

这将立即为您提供列表。

在存储过程中也可以使用循环，但出于语法原因，您必须使用WHILE：

CREATE PROCEDURE someProcedure(IN start_year INT, end_year INT) 
BEGIN
  DECLARE v_year_id INT;
  SET v_year_id=start_year;
  WHILE(v_year_id<end_year)
  LOOP
    select  B.YearID, sum(B.ab), sum(B.h), sum(B.h)/ sum(B.ab)
    From Batting B join Pitching P 
    on (P.playerID = B.playerID and B.yearID = P.yearid and B.ab > 0 ) 
    WHERE yearId=v_year_id;
    group by B.yearid; 
    SET v_year_id=v_year_id+1;
  END WHILE;
END;

也可以删除局部变量v_year_id，但为了清楚起见，此处已添加。如果消除v_year_id，它将如下所示：

CREATE PROCEDURE someProcedure(IN start_year INT, end_year INT) 
BEGIN
  WHILE(start_year<end_year)
  LOOP
    select  B.YearID, sum(B.ab), sum(B.h), sum(B.h)/ sum(B.ab)
    From Batting B join Pitching P 
    on (P.playerID = B.playerID and B.yearID = P.yearid and B.ab > 0 ) 
    WHERE yearId=start_year;
    group by B.yearid; 
    SET start_year=start_year+1;
  END WHILE;
END;

调用程序将通过以下方式完成：

CALL someProcedure(2011,2014);

MySQL Query循环HELP，不使用PHP

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