Question

我希望能够在SQL中将数字舍入为n个有效数字。所以：

123.456 rounded to 2sf would give 120
0.00123 rounded to 2sf would give 0.0012

我知道ROUND（）函数，它舍入到n个小数位而不是有效数字。

Answer 1

select round(@number,@sf-1- floor(log10(abs(@number))))应该做到这一点！

成功测试了两个例子。

编辑：在@ number = 0上调用此函数将不起作用。在使用此代码之前，您应该为此添加测试。

create function sfround(@number float, @sf int) returns float as
begin
    declare @r float
    select @r = case when @number = 0 then 0 else round(@number ,@sf -1-floor(log10(abs(@number )))) end
    return (@r)
end

Answer 2

将Brann最流行的答案改编成MySQL，让那些看起来像我的人。

CREATE FUNCTION `sfround`(num FLOAT, sf INT) # creates the function
RETURNS float # defines output type
DETERMINISTIC # given input, will return same output

BEGIN

    DECLARE r FLOAT;  # make a variable called r, defined as a float

    IF( num IS NULL OR num = 0) THEN # ensure the number exists, and isn't 0
        SET r = num; # if it is; leave alone

    ELSE
        SET r = ROUND(num, sf - 1 - FLOOR(LOG10(ABS(num))));
    /* see below*/
    END IF;

    RETURN (r);

END

/ *感觉太长，无法发表评论* /

ROUND（num，sf - 1 - FLOOR（LOG10（ABS（num））））

执行工作的部分 - 正常使用数字上的ROUND函数，但计算要舍入的长度
ABS确保正面
LOG10获取数字
FLOOR获取小于结果数
因此总是向下舍入并给出一个整数
sf - 1 - FLOOR（...）给出负数
有效，因为ROUND（num，-ve num）向小数点左侧舍入
仅一次性，ROUND（123.456，-1）和ROUND（0.00123,4）返回所要求的答案（（120,0.0012）

Answer 3

你可以在四舍五入之前除以100然后再乘以100 ......

Answer 4

我想我已经成功了。

CREATE FUNCTION RoundSigFig(@Number float, @Figures int)
RETURNS float
AS
BEGIN

    DECLARE @Answer float;

    SET @Answer = (
    SELECT
        CASE WHEN intPower IS NULL THEN 0
        ELSE FLOOR(fltNumber * POWER(CAST(10 AS float), intPower) + 0.5) 
                * POWER(CAST(10 AS float), -intPower)
        END AS ans
    FROM (
        SELECT
            @Number AS fltNumber,
            CASE WHEN @Number > 0
                THEN -((CEILING(LOG10(@Number)) - @Figures))
            WHEN @Number < 0
                THEN -((FLOOR(LOG10(@Number)) - @Figures))
            ELSE NULL END AS intPower       
        ) t
    );

    RETURN @Answer;
END

在SQL中舍入到n个重要数字

4 个答案: