Question

Is there a neat way to apply a mask to a string in a SQL Server query?

I have two tables, one with Phone number stored as varchar with no literals 0155567890 and a phone type, which has a mask for that phone number type: (##) #### ####

What is the best way to return a string (for a merge Document) so that the query returns the fully formatted phone number:

[phone]

Answer 1

As noted in the comment, my original answer below will result in terrible performance if used in a large number of rows. i-one’s answer is preferred if performance is a consideration.

I needed this also, and thanks to Sjuul’s pseudocode, I was able to create a function to do this.

CREATE FUNCTION [dbo].[fx_FormatUsingMask] 
(
    -- Add the parameters for the function here
    @input nvarchar(1000),
    @mask nvarchar(1000)
)
RETURNS nvarchar(1000)
AS
BEGIN
    -- Declare the return variable here
    DECLARE @result nvarchar(1000) = ''
    DECLARE @inputPos int = 1
    DECLARE @maskPos int = 1
    DECLARE @maskSign char(1) = ''

    WHILE @maskPos <= Len(@mask)
    BEGIN
        set @maskSign = substring(@mask, @maskPos, 1)

        IF @maskSign = '#'
        BEGIN
            set @result = @result + substring(@input, @inputPos, 1)
            set @inputPos += 1
            set @maskPos += 1
        END
        ELSE
        BEGIN
            set @result = @result + @maskSign
            set @maskPos += 1
        END
    END
    -- Return the result of the function
    RETURN @result

END