SQL Server functions are powerful tools that allow developers to perform various calculations and manipulations on data. In this article, we will explore the concept of rounding a number to the first two significant places using SQL Server functions.

Let’s start by creating some tests to ensure our function works correctly. We will create a result set with two columns – the expected result and the actual result. This will help us verify the accuracy of our function.

SELECT * FROM
(
    SELECT 0.243 AS param, dbo.roundToSignificant(0.243, 2) AS result, 0.24 AS expected
    UNION ALL
    SELECT 0.00592, dbo.roundToSignificant(0.00592, 2), 0.0059
    UNION ALL
    SELECT 34600, dbo.roundToSignificant(34600, 2), 35000
    UNION ALL
    SELECT -3323, dbo.roundToSignificant(-3323, 2), -3300
    UNION ALL
    SELECT -3.59, dbo.roundToSignificant(-3.59, 2), -3.6
) t
WHERE t.result <> t.expected

Now that we have our tests set up, let’s create the function. We will use the ROUND function in SQL Server to round the number to the desired number of decimal places. To determine the number of decimal places, we will use the LOG10 function.

CREATE FUNCTION dbo.roundToSignificant(@num FLOAT, @significantPlaces INT) RETURNS FLOAT AS
BEGIN
    DECLARE @res FLOAT
    SELECT @res = ROUND(@num, @significantPlaces - 1 - FLOOR(LOG10(ABS(@num))))
    RETURN (@res)
END

Now, let’s run our test query again to see if our function produces the expected results. If no rows are returned, it means our function is working correctly.

It’s important to note that using the FLOAT data type in our function may produce incorrect results for certain values. To address this, we can use the NUMERIC data type instead. Additionally, we can handle the case of zero by checking if the number is equal to zero before performing any calculations.

CREATE FUNCTION dbo.roundToSignificant(@num NUMERIC(36, 18), @significantPlaces INT) RETURNS NUMERIC(36, 18) AS
BEGIN
    RETURN (
        CASE
            WHEN @num = 0 THEN 0
            ELSE ROUND(@num, @significantPlaces - 1 - FLOOR(LOG10(ABS(@num))))
        END
    )
END

Now our function is more robust and can handle a wider range of values. It’s always important to consider the data types and potential edge cases when working with functions in SQL Server.

In conclusion, SQL Server functions are powerful tools that allow developers to perform complex calculations and manipulations on data. By understanding the concepts behind these functions and how to use them effectively, developers can enhance their SQL Server skills and create more efficient and accurate queries.