T-SQLで文字列をURLエンコードするロジック

This is test. !"#$%&''()-=^~\|@`[{;+:*]},<.>/?\_

↑こんなのが

%54%68%69%73%20%69%73%20%74%65%73%74%2e%20%21%22%23%24%25%26%27%28%29%2d%3d%5e%7e%5c%7c%40%60%5b%7b%3b%2b%3a%2a%5d%7d%2c%3c%2e%3e%2f%3f%5c%5f

↑こんな感じに変換されます。

ただし制限事項ありです。

入力文字はASCII文字限定です。日本語は入力不可です。
Outputは最大4000文字です。それを超える場合の動作は分かりません (^_^;

--ORIGINAL VALUE
DECLARE @str VARCHAR(4000)
SELECT @str = 'This is test. !"#$%&''()-=^~\|@`[{;+:*]},<.>/?\_'

--DECLARE AND INITIALIZE VARIABLES
DECLARE @curr INT,
        @end  INT,
        @out  VARCHAR(4000)
SELECT @curr = 0 ,
       @end = LEN(@str),
       @out = ''

--CONVERT EACH CHARACTER TO ENCODED CHARACTER
WHILE @curr <= @end
BEGIN
        DECLARE @target  nvarchar(1),
                @unicode INT,
                @binary  VARCHAR(10)             

        SELECT @target = SUBSTRING(@str, @curr, @curr + 1)
        SELECT @unicode = UNICODE(@target)
        --http://yakumo80.blog33.fc2.com/blog-entry-409.html
        SELECT @binary = STUFF((master.dbo.fn_varbintohexstr(
                           CAST(CAST(@unicode AS BIGINT) AS BINARY(1))) 
                           COLLATE Latin1_General_CI_AS_KS_WS ), 1, 2, '')
        SELECT @out = ISNULL(@out, '') + '%' + @binary
        
        SELECT @curr = @curr + 1
END

--DISPLAY RESULT
--E.G. '%54%68%69%73%20%69%73%20%74%65%73%74%2e%20%21%22%23%24%25%26%27%28%29%2d%3d%5e%7e%5c%7c%40%60%5b%7b%3b%2b%3a%2a%5d%7d%2c%3c%2e%3e%2f%3f%5c%5f'
SELECT @out