T-SQL Space Before Capital Letters

Question

The question is self explanatory. Could you please point out a way to put spaces between each capital letter of a string.

SELECT dbo.SpaceBeforeCap('ThisIsATestString')

would result in

This Is A Test String.

Answer 1

This function combines previous answers. Selectively choose to preserve adjacent CAPS:

CREATE FUNCTION SpaceBeforeCap (
    @InputString NVARCHAR(MAX),
    @PreserveAdjacentCaps BIT
)
RETURNS NVARCHAR(MAX)
AS
BEGIN

DECLARE
    @i INT, @j INT,
        @previous NCHAR, @current NCHAR, @next NCHAR,
        @result NVARCHAR(MAX)

SELECT
    @i = 1,
        @j = LEN(@InputString),
        @result = ''

WHILE @i <= @j
BEGIN
    SELECT
        @previous = SUBSTRING(@InputString,@i-1,1),
                @current = SUBSTRING(@InputString,@i+0,1),
                @next = SUBSTRING(@InputString,@i+1,1)

    IF @current = UPPER(@current) COLLATE Latin1_General_CS_AS
    BEGIN
        -- Add space if Current is UPPER 
        -- and either Previous or Next is lower or user chose not to preserve adjacent caps
        -- and Previous or Current is not already a space
        IF @current = UPPER(@current) COLLATE Latin1_General_CS_AS
        AND (
                            @previous <> UPPER(@previous) COLLATE Latin1_General_CS_AS
                            OR  @next <> UPPER(@next) collate Latin1_General_CS_AS
                            OR  @PreserveAdjacentCaps = 0
        )
        AND @previous <> ' '
        AND @current <> ' '
            SET @result = @result + ' '
    END 

    SET @result = @result + @current
    SET @i = @i + 1
END 

RETURN @result
END

GO
SELECT dbo.SpaceBeforeCap('ThisIsASampleDBString', 1)
GO
SELECT dbo.SpaceBeforeCap('ThisIsASampleDBString', 0)