sqlserver 中文base64编解码

1.前言。
   如题，编解码格式都为gbk。编码可以不用函数。直接用for xml 。如：
SELECT (SELECT CONVERT(varbinary(max), '分为服务') FOR XML PATH(''), TYPE).value('/', 'nvarchar(max)')
2.解码。

CREATE FUNCTION dbo.base64_decode
(
@encoded_text varchar(max)
)
RETURNS varbinary(max)
AS
BEGIN
DECLARE
    @output varbinary(max),
    @block_start int,
    @encoded_length int,
    @decoded_length int,
    @mapr binary(122)
IF LEN(@encoded_text) & 3 > 0
    OR @encoded_text LIKE '%[^ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=]%' COLLATE Latin1_General_Bin
    RETURN NULL
SET @output = 0x
-- The nth byte of @mapr contains the base64 value of the character with an ASCII value of n.
-- eg. 65th byte = 0x00 = 0 = value of 'A'
SET @mapr =
          0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF -- 1-33
        + 0xFFFFFFFFFFFFFFFFFFFF3EFFFFFF3F3435363738393A3B3C3DFFFFFF00FFFFFF -- 33-64
        + 0x000102030405060708090A0B0C0D0E0F10111213141516171819FFFFFFFFFFFF -- 65-96
        + 0x1A1B1C1D1E1F202122232425262728292A2B2C2D2E2F30313233 -- 97-122
--get the number of blocks to be decoded
SET @encoded_length = LEN(@encoded_text)
SET @decoded_length = @encoded_length / 4 * 3
--for each block
SET @block_start = 1
WHILE @block_start < @encoded_length
BEGIN
    --decode the block and add to output
    --BINARY values between 1 and 4 bytes can be implicitly cast to INT
    SET @output = @output +
        CAST(CAST(
              SUBSTRING(@mapr, ASCII(SUBSTRING(@encoded_text, @block_start    , 1)), 1) * 262144
            + SUBSTRING(@mapr, ASCII(SUBSTRING(@encoded_text, @block_start + 1, 1)), 1) * 4096
            + SUBSTRING(@mapr, ASCII(SUBSTRING(@encoded_text, @block_start + 2, 1)), 1) * 64
            + SUBSTRING(@mapr, ASCII(SUBSTRING(@encoded_text, @block_start + 3, 1)), 1)
        AS int) AS binary(3))
    SET @block_start = @block_start + 4
END
IF RIGHT(@encoded_text, 2) = '=='
    SET @decoded_length = @decoded_length - 2
ELSE IF RIGHT(@encoded_text, 1) = '='
    SET @decoded_length = @decoded_length - 1
RETURN SUBSTRING(@output, 1, @decoded_length)
END

测试:select convert(varchar(2000),dbo.base64_decode('t9bOqrf+zvE=')  )
测试结果为:分为服务
3.注意事项。
  （1）编解码用utf-8毫无意义，以上都是针对gbk,utf-8的可以在网上找下，utf-8的和gbk的编解码方式不同。