Format value to configured number of decimal places I want to format a number to display decimal places according to a configuration value specified in another table. If the configured value is NULL, the number of decimal places should default to 2 (hardcoded here) The following statement works fine except that for values like 3.50000 which returns 3.5 even when the configured value for 'NumberOfDecimalPlaces' is 2 or 3. I get that it is the desired behavior for ROUND()

ROUND([ActualValue], COALESCE([ConfigurationTable].[NumberOfDecimalPlaces], 2)) [FormattedActualValue]


As an alternative, I tried CONVERT AND CAST. 

SELECT CAST ([ActualValue] AS NUMERIC(16, COALESCE([ConfigurationTable].[NumberOfDecimalPlaces], 2))

SELECT CONVERT(DECIMAL (16, COALESCE([ConfigurationTable].[NumberOfDecimalPlaces], 2)), [ActualValue])


Both of which err to Incorrect syntax near the keyword 'COALESCE'. I understand that the second parameter to the datatype definition is not nullable and hence the error. What are my options? How can I achieve this with minimum performance overhead?
The STR function seems to be what you're looking for:

DECLARE @NumberOfDecimalPlaces tinyint = 3;
DECLARE @ActualValue decimal(16,5) =  3.50

SELECT FormattedActualValue = 
    STR(
        @ActualValue, 
        CAST(@ActualValue / 10 AS int) + @NumberOfDecimalPlaces + 2,
        COALESCE(@NumberOfDecimalPlaces,2)
    )