Round to n Significant Figures in SQL

Question

I would like to be able to round a number to n significant figures in SQL. So:

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


        

Answer 1

I think I've managed it.

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